diff --git a/backend/app/api/v1/members.py b/backend/app/api/v1/members.py
new file mode 100644
index 00000000..31e1e3f1
--- /dev/null
+++ b/backend/app/api/v1/members.py
@@ -0,0 +1,90 @@
+import uuid
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.deps import get_db_session, require_study_member, require_study_roles
+from app.crud import member as member_crud
+from app.crud import study as study_crud
+from app.schemas.member import StudyMemberCreate, StudyMemberRead, StudyMemberUpdate
+
+router = APIRouter()
+
+
+async def _ensure_study_exists(db: AsyncSession, study_id: uuid.UUID):
+    study = await study_crud.get(db, study_id)
+    if not study:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Study not found")
+    return study
+
+
+@router.post(
+    "/",
+    response_model=StudyMemberRead,
+    status_code=status.HTTP_201_CREATED,
+    dependencies=[Depends(require_study_roles(["PM"]))],
+)
+async def add_member(
+    study_id: uuid.UUID,
+    member_in: StudyMemberCreate,
+    db: AsyncSession = Depends(get_db_session),
+) -> StudyMemberRead:
+    await _ensure_study_exists(db, study_id)
+    existing = await member_crud.get_member(db, study_id, member_in.user_id)
+    if existing:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Member already exists")
+    member = await member_crud.add_member(db, study_id, member_in)
+    return member
+
+
+@router.get(
+    "/",
+    response_model=list[StudyMemberRead],
+    dependencies=[Depends(require_study_member())],
+)
+async def list_members(
+    study_id: uuid.UUID,
+    skip: int = 0,
+    limit: int = 100,
+    db: AsyncSession = Depends(get_db_session),
+) -> list[StudyMemberRead]:
+    await _ensure_study_exists(db, study_id)
+    members = await member_crud.list_members(db, study_id, skip=skip, limit=limit)
+    return list(members)
+
+
+@router.patch(
+    "/{member_id}",
+    response_model=StudyMemberRead,
+    dependencies=[Depends(require_study_roles(["PM"]))],
+)
+async def update_member(
+    study_id: uuid.UUID,
+    member_id: uuid.UUID,
+    member_in: StudyMemberUpdate,
+    db: AsyncSession = Depends(get_db_session),
+) -> StudyMemberRead:
+    await _ensure_study_exists(db, study_id)
+    member = await member_crud.get_member_by_id(db, member_id)
+    if not member or member.study_id != study_id:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Member not found")
+    updated = await member_crud.update_member(db, member, member_in)
+    return updated
+
+
+@router.delete(
+    "/{member_id}",
+    response_model=StudyMemberRead,
+    dependencies=[Depends(require_study_roles(["PM"]))],
+)
+async def remove_member(
+    study_id: uuid.UUID,
+    member_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db_session),
+) -> StudyMemberRead:
+    await _ensure_study_exists(db, study_id)
+    member = await member_crud.get_member_by_id(db, member_id)
+    if not member or member.study_id != study_id:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Member not found")
+    removed = await member_crud.remove_member(db, member)
+    return removed
diff --git a/backend/app/api/v1/router.py b/backend/app/api/v1/router.py
index a30bc091..7b77b492 100644
--- a/backend/app/api/v1/router.py
+++ b/backend/app/api/v1/router.py
@@ -1,7 +1,10 @@
 from fastapi import APIRouter
 
-from app.api.v1 import auth, users
+from app.api.v1 import auth, users, studies, sites, members
 
 api_router = APIRouter()
 api_router.include_router(auth.router, prefix="/auth", tags=["auth"])
 api_router.include_router(users.router, prefix="/users", tags=["users"])
+api_router.include_router(studies.router, prefix="/studies", tags=["studies"])
+api_router.include_router(sites.router, prefix="/studies/{study_id}/sites", tags=["sites"])
+api_router.include_router(members.router, prefix="/studies/{study_id}/members", tags=["study-members"])
diff --git a/backend/app/api/v1/sites.py b/backend/app/api/v1/sites.py
new file mode 100644
index 00000000..c6bdb4e8
--- /dev/null
+++ b/backend/app/api/v1/sites.py
@@ -0,0 +1,69 @@
+import uuid
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.deps import get_db_session, require_study_member, require_study_roles
+from app.crud import site as site_crud
+from app.crud import study as study_crud
+from app.schemas.site import SiteCreate, SiteRead, SiteUpdate
+
+router = APIRouter()
+
+
+async def _ensure_study_exists(db: AsyncSession, study_id: uuid.UUID):
+    study = await study_crud.get(db, study_id)
+    if not study:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Study not found")
+    return study
+
+
+@router.post(
+    "/",
+    response_model=SiteRead,
+    status_code=status.HTTP_201_CREATED,
+    dependencies=[Depends(require_study_roles(["PM"]))],
+)
+async def create_site(
+    study_id: uuid.UUID,
+    site_in: SiteCreate,
+    db: AsyncSession = Depends(get_db_session),
+) -> SiteRead:
+    await _ensure_study_exists(db, study_id)
+    site = await site_crud.create_site(db, study_id, site_in)
+    return site
+
+
+@router.get(
+    "/",
+    response_model=list[SiteRead],
+    dependencies=[Depends(require_study_member())],
+)
+async def list_sites(
+    study_id: uuid.UUID,
+    skip: int = 0,
+    limit: int = 100,
+    db: AsyncSession = Depends(get_db_session),
+) -> list[SiteRead]:
+    await _ensure_study_exists(db, study_id)
+    sites = await site_crud.list_by_study(db, study_id, skip=skip, limit=limit)
+    return list(sites)
+
+
+@router.patch(
+    "/{site_id}",
+    response_model=SiteRead,
+    dependencies=[Depends(require_study_roles(["PM"]))],
+)
+async def update_site(
+    study_id: uuid.UUID,
+    site_id: uuid.UUID,
+    site_in: SiteUpdate,
+    db: AsyncSession = Depends(get_db_session),
+) -> SiteRead:
+    await _ensure_study_exists(db, study_id)
+    site = await site_crud.get_site(db, site_id)
+    if not site or site.study_id != study_id:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Site not found")
+    updated = await site_crud.update_site(db, site, site_in)
+    return updated
diff --git a/backend/app/api/v1/studies.py b/backend/app/api/v1/studies.py
new file mode 100644
index 00000000..029246a0
--- /dev/null
+++ b/backend/app/api/v1/studies.py
@@ -0,0 +1,65 @@
+import uuid
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.deps import get_current_user, get_db_session, require_roles, require_study_member, require_study_roles
+from app.crud import study as study_crud
+from app.schemas.study import StudyCreate, StudyRead, StudyUpdate
+
+router = APIRouter()
+
+
+@router.post("/", response_model=StudyRead, status_code=status.HTTP_201_CREATED, dependencies=[Depends(require_roles(["ADMIN"]))])
+async def create_study(
+    study_in: StudyCreate,
+    db: AsyncSession = Depends(get_db_session),
+    current_user=Depends(get_current_user),
+) -> StudyRead:
+    existing = await study_crud.get_by_code(db, study_in.code)
+    if existing:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Study code already exists")
+    study = await study_crud.create(db, study_in, created_by=current_user.id)
+    return study
+
+
+@router.get("/", response_model=list[StudyRead])
+async def list_studies(
+    skip: int = 0,
+    limit: int = 100,
+    db: AsyncSession = Depends(get_db_session),
+    current_user=Depends(get_current_user),
+) -> list[StudyRead]:
+    if current_user.role == "ADMIN":
+        studies = await study_crud.list_studies(db, skip=skip, limit=limit)
+    else:
+        studies = await study_crud.list_studies_for_user(db, current_user.id, skip=skip, limit=limit)
+    return list(studies)
+
+
+@router.get("/{study_id}", response_model=StudyRead, dependencies=[Depends(require_study_member())])
+async def get_study(
+    study_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db_session),
+) -> StudyRead:
+    study = await study_crud.get(db, study_id)
+    if not study:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Study not found")
+    return study
+
+
+@router.patch(
+    "/{study_id}",
+    response_model=StudyRead,
+    dependencies=[Depends(require_study_roles(["PM"]))],
+)
+async def update_study(
+    study_id: uuid.UUID,
+    study_in: StudyUpdate,
+    db: AsyncSession = Depends(get_db_session),
+) -> StudyRead:
+    study = await study_crud.get(db, study_id)
+    if not study:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Study not found")
+    updated = await study_crud.update(db, study, study_in)
+    return updated
diff --git a/backend/app/core/deps.py b/backend/app/core/deps.py
index d2ceca90..69c64aa6 100644
--- a/backend/app/core/deps.py
+++ b/backend/app/core/deps.py
@@ -7,6 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.security import decode_token, oauth2_scheme
 from app.crud import user as user_crud
+from app.crud import member as member_crud
 from app.db.session import SessionLocal
 from app.schemas.user import TokenPayload
 
@@ -52,3 +53,53 @@ def require_roles(roles: Iterable[str]) -> Callable:
         return current_user
 
     return dependency
+
+
+async def get_study_member(
+    study_id: uuid.UUID,
+    current_user=Depends(get_current_user),
+    db: AsyncSession = Depends(get_db_session),
+):
+    if current_user.role == "ADMIN":
+        return None
+    return await member_crud.get_member(db, study_id, current_user.id)
+
+
+def require_study_member():
+    async def dependency(
+        study_id: uuid.UUID,
+        current_user=Depends(get_current_user),
+        db: AsyncSession = Depends(get_db_session),
+    ):
+        if current_user.role == "ADMIN":
+            return current_user
+        membership = await member_crud.get_member(db, study_id, current_user.id)
+        if not membership or not membership.is_active:
+            raise HTTPException(
+                status_code=status.HTTP_403_FORBIDDEN,
+                detail="Not a member of this study",
+            )
+        return current_user
+
+    return dependency
+
+
+def require_study_roles(roles: Iterable[str]):
+    roles_set = set(roles)
+
+    async def dependency(
+        study_id: uuid.UUID,
+        current_user=Depends(get_current_user),
+        db: AsyncSession = Depends(get_db_session),
+    ):
+        if current_user.role == "ADMIN":
+            return current_user
+        membership = await member_crud.get_member(db, study_id, current_user.id)
+        if not membership or not membership.is_active or membership.role_in_study not in roles_set:
+            raise HTTPException(
+                status_code=status.HTTP_403_FORBIDDEN,
+                detail="Insufficient study permissions",
+            )
+        return current_user
+
+    return dependency
diff --git a/backend/app/crud/member.py b/backend/app/crud/member.py
new file mode 100644
index 00000000..24db02a6
--- /dev/null
+++ b/backend/app/crud/member.py
@@ -0,0 +1,64 @@
+import uuid
+from typing import Sequence
+
+from sqlalchemy import select, update
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.study_member import StudyMember
+from app.schemas.member import StudyMemberCreate, StudyMemberUpdate
+
+
+async def get_member(db: AsyncSession, study_id: uuid.UUID, user_id: uuid.UUID) -> StudyMember | None:
+    result = await db.execute(
+        select(StudyMember).where(StudyMember.study_id == study_id, StudyMember.user_id == user_id)
+    )
+    return result.scalar_one_or_none()
+
+
+async def get_member_by_id(db: AsyncSession, member_id: uuid.UUID) -> StudyMember | None:
+    result = await db.execute(select(StudyMember).where(StudyMember.id == member_id))
+    return result.scalar_one_or_none()
+
+
+async def add_member(db: AsyncSession, study_id: uuid.UUID, member_in: StudyMemberCreate) -> StudyMember:
+    member = StudyMember(
+        study_id=study_id,
+        user_id=member_in.user_id,
+        role_in_study=member_in.role_in_study,
+        is_active=member_in.is_active,
+    )
+    db.add(member)
+    await db.commit()
+    await db.refresh(member)
+    return member
+
+
+async def list_members(db: AsyncSession, study_id: uuid.UUID, skip: int = 0, limit: int = 100) -> Sequence[StudyMember]:
+    result = await db.execute(
+        select(StudyMember).where(StudyMember.study_id == study_id).offset(skip).limit(limit)
+    )
+    return result.scalars().all()
+
+
+async def update_member(db: AsyncSession, member: StudyMember, member_in: StudyMemberUpdate) -> StudyMember:
+    update_data = {k: v for k, v in member_in.model_dump(exclude_unset=True).items() if v is not None}
+    if update_data:
+        await db.execute(
+            update(StudyMember)
+            .where(StudyMember.id == member.id)
+            .values(**update_data)
+        )
+        await db.commit()
+    await db.refresh(member)
+    return member
+
+
+async def remove_member(db: AsyncSession, member: StudyMember) -> StudyMember:
+    await db.execute(
+        update(StudyMember)
+        .where(StudyMember.id == member.id)
+        .values(is_active=False)
+    )
+    await db.commit()
+    await db.refresh(member)
+    return member
diff --git a/backend/app/crud/site.py b/backend/app/crud/site.py
new file mode 100644
index 00000000..69b79ed4
--- /dev/null
+++ b/backend/app/crud/site.py
@@ -0,0 +1,48 @@
+import uuid
+from typing import Sequence
+
+from sqlalchemy import select, update
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.site import Site
+from app.schemas.site import SiteCreate, SiteUpdate
+
+
+async def create_site(db: AsyncSession, study_id: uuid.UUID, site_in: SiteCreate) -> Site:
+    site = Site(
+        study_id=study_id,
+        name=site_in.name,
+        city=site_in.city,
+        pi_name=site_in.pi_name,
+        contact=site_in.contact,
+        is_active=site_in.is_active,
+    )
+    db.add(site)
+    await db.commit()
+    await db.refresh(site)
+    return site
+
+
+async def get_site(db: AsyncSession, site_id: uuid.UUID) -> Site | None:
+    result = await db.execute(select(Site).where(Site.id == site_id))
+    return result.scalar_one_or_none()
+
+
+async def update_site(db: AsyncSession, site: Site, site_in: SiteUpdate) -> Site:
+    update_data = site_in.model_dump(exclude_unset=True)
+    if update_data:
+        await db.execute(
+            update(Site)
+            .where(Site.id == site.id)
+            .values(**update_data)
+        )
+        await db.commit()
+    await db.refresh(site)
+    return site
+
+
+async def list_by_study(db: AsyncSession, study_id: uuid.UUID, skip: int = 0, limit: int = 100) -> Sequence[Site]:
+    result = await db.execute(
+        select(Site).where(Site.study_id == study_id).offset(skip).limit(limit)
+    )
+    return result.scalars().all()
diff --git a/backend/app/crud/study.py b/backend/app/crud/study.py
new file mode 100644
index 00000000..f3e4a130
--- /dev/null
+++ b/backend/app/crud/study.py
@@ -0,0 +1,71 @@
+import uuid
+from typing import Sequence
+
+from sqlalchemy import select, update
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.study import Study
+from app.schemas.study import StudyCreate, StudyUpdate
+
+
+async def create(db: AsyncSession, study_in: StudyCreate, *, created_by: uuid.UUID | None = None) -> Study:
+    study = Study(
+        code=study_in.code,
+        name=study_in.name,
+        sponsor=study_in.sponsor,
+        protocol_no=study_in.protocol_no,
+        phase=study_in.phase,
+        status=study_in.status,
+        created_by=created_by,
+    )
+    db.add(study)
+    await db.commit()
+    await db.refresh(study)
+    return study
+
+
+async def get(db: AsyncSession, study_id: uuid.UUID) -> Study | None:
+    result = await db.execute(select(Study).where(Study.id == study_id))
+    return result.scalar_one_or_none()
+
+
+async def get_by_code(db: AsyncSession, code: str) -> Study | None:
+    result = await db.execute(select(Study).where(Study.code == code))
+    return result.scalar_one_or_none()
+
+
+async def update(db: AsyncSession, study: Study, study_in: StudyUpdate) -> Study:
+    update_data = study_in.model_dump(exclude_unset=True)
+    if update_data:
+        await db.execute(
+            update(Study)
+            .where(Study.id == study.id)
+            .values(**update_data)
+        )
+        await db.commit()
+    await db.refresh(study)
+    return study
+
+
+async def list_studies(db: AsyncSession, skip: int = 0, limit: int = 100) -> Sequence[Study]:
+    result = await db.execute(select(Study).offset(skip).limit(limit))
+    return result.scalars().all()
+
+
+async def list_studies_for_user(
+    db: AsyncSession,
+    user_id: uuid.UUID,
+    skip: int = 0,
+    limit: int = 100,
+) -> Sequence[Study]:
+    from app.models.study_member import StudyMember  # local import to avoid cycles
+
+    stmt = (
+        select(Study)
+        .join(StudyMember, StudyMember.study_id == Study.id)
+        .where(StudyMember.user_id == user_id, StudyMember.is_active.is_(True))
+        .offset(skip)
+        .limit(limit)
+    )
+    result = await db.execute(stmt)
+    return result.scalars().all()
diff --git a/backend/app/db/base.py b/backend/app/db/base.py
index fa2b68a5..0b1a63b7 100644
--- a/backend/app/db/base.py
+++ b/backend/app/db/base.py
@@ -1,5 +1,7 @@
-from sqlalchemy.orm import DeclarativeBase
+from app.db.base_class import Base
 
-
-class Base(DeclarativeBase):
-    pass
+# Import models to ensure metadata is loaded for create_all
+from app.models.user import User  # noqa: F401
+from app.models.study import Study  # noqa: F401
+from app.models.site import Site  # noqa: F401
+from app.models.study_member import StudyMember  # noqa: F401
diff --git a/backend/app/db/base_class.py b/backend/app/db/base_class.py
new file mode 100644
index 00000000..fa2b68a5
--- /dev/null
+++ b/backend/app/db/base_class.py
@@ -0,0 +1,5 @@
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    pass
diff --git a/backend/app/models/site.py b/backend/app/models/site.py
new file mode 100644
index 00000000..c92035cd
--- /dev/null
+++ b/backend/app/models/site.py
@@ -0,0 +1,21 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, String, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base_class import Base
+
+
+class Site(Base):
+    __tablename__ = "sites"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    study_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("studies.id"), index=True, nullable=False)
+    name: Mapped[str] = mapped_column(String(200), nullable=False)
+    city: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    pi_name: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    contact: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, server_default="true")
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now())
diff --git a/backend/app/models/study.py b/backend/app/models/study.py
new file mode 100644
index 00000000..4748004d
--- /dev/null
+++ b/backend/app/models/study.py
@@ -0,0 +1,22 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, String, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base_class import Base
+
+
+class Study(Base):
+    __tablename__ = "studies"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    code: Mapped[str] = mapped_column(String(50), unique=True, nullable=False, index=True)
+    name: Mapped[str] = mapped_column(String(200), nullable=False)
+    sponsor: Mapped[str | None] = mapped_column(String(200), nullable=True)
+    protocol_no: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    phase: Mapped[str | None] = mapped_column(String(50), nullable=True)
+    status: Mapped[str] = mapped_column(String(20), nullable=False, default="DRAFT")
+    created_by: Mapped[uuid.UUID | None] = mapped_column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now())
diff --git a/backend/app/models/study_member.py b/backend/app/models/study_member.py
new file mode 100644
index 00000000..5ed2f2fd
--- /dev/null
+++ b/backend/app/models/study_member.py
@@ -0,0 +1,20 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, String, UniqueConstraint, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base_class import Base
+
+
+class StudyMember(Base):
+    __tablename__ = "study_members"
+    __table_args__ = (UniqueConstraint("study_id", "user_id", name="uq_study_member"),)
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    study_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("studies.id"), nullable=False, index=True)
+    user_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=False)
+    role_in_study: Mapped[str] = mapped_column(String(20), nullable=False)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, server_default="true")
+    added_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now())
diff --git a/backend/app/models/user.py b/backend/app/models/user.py
index 50e5e1b5..96851aa2 100644
--- a/backend/app/models/user.py
+++ b/backend/app/models/user.py
@@ -5,7 +5,7 @@ from sqlalchemy import Boolean, DateTime, String, func
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column
 
-from app.db.base import Base
+from app.db.base_class import Base
 
 
 class User(Base):
diff --git a/backend/app/schemas/member.py b/backend/app/schemas/member.py
new file mode 100644
index 00000000..0fa7935c
--- /dev/null
+++ b/backend/app/schemas/member.py
@@ -0,0 +1,29 @@
+import uuid
+from datetime import datetime
+from typing import Literal, Optional
+
+from pydantic import BaseModel, ConfigDict, Field
+
+StudyRole = Literal["PM", "CRA", "PV", "IMP"]
+
+
+class StudyMemberCreate(BaseModel):
+    user_id: uuid.UUID
+    role_in_study: StudyRole
+    is_active: bool = True
+
+
+class StudyMemberUpdate(BaseModel):
+    role_in_study: Optional[StudyRole] = None
+    is_active: Optional[bool] = None
+
+
+class StudyMemberRead(BaseModel):
+    id: uuid.UUID
+    study_id: uuid.UUID
+    user_id: uuid.UUID
+    role_in_study: StudyRole
+    is_active: bool
+    added_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
diff --git a/backend/app/schemas/site.py b/backend/app/schemas/site.py
new file mode 100644
index 00000000..d66a7c2d
--- /dev/null
+++ b/backend/app/schemas/site.py
@@ -0,0 +1,34 @@
+import uuid
+from datetime import datetime
+from typing import Optional
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class SiteCreate(BaseModel):
+    name: str = Field(min_length=1)
+    city: Optional[str] = None
+    pi_name: Optional[str] = None
+    contact: Optional[str] = None
+    is_active: bool = True
+
+
+class SiteUpdate(BaseModel):
+    name: Optional[str] = None
+    city: Optional[str] = None
+    pi_name: Optional[str] = None
+    contact: Optional[str] = None
+    is_active: Optional[bool] = None
+
+
+class SiteRead(BaseModel):
+    id: uuid.UUID
+    study_id: uuid.UUID
+    name: str
+    city: Optional[str]
+    pi_name: Optional[str]
+    contact: Optional[str]
+    is_active: bool
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
diff --git a/backend/app/schemas/study.py b/backend/app/schemas/study.py
new file mode 100644
index 00000000..1bda9bbf
--- /dev/null
+++ b/backend/app/schemas/study.py
@@ -0,0 +1,39 @@
+import uuid
+from datetime import datetime
+from typing import Literal, Optional
+
+from pydantic import BaseModel, ConfigDict, Field
+
+StudyStatus = Literal["DRAFT", "ACTIVE", "CLOSED"]
+
+
+class StudyCreate(BaseModel):
+    code: str = Field(min_length=1)
+    name: str = Field(min_length=1)
+    sponsor: Optional[str] = None
+    protocol_no: Optional[str] = None
+    phase: Optional[str] = None
+    status: StudyStatus = "DRAFT"
+
+
+class StudyUpdate(BaseModel):
+    code: Optional[str] = None
+    name: Optional[str] = None
+    sponsor: Optional[str] = None
+    protocol_no: Optional[str] = None
+    phase: Optional[str] = None
+    status: Optional[StudyStatus] = None
+
+
+class StudyRead(BaseModel):
+    id: uuid.UUID
+    code: str
+    name: str
+    sponsor: Optional[str]
+    protocol_no: Optional[str]
+    phase: Optional[str]
+    status: StudyStatus
+    created_by: Optional[uuid.UUID]
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
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