diff --git a/changelog.md b/changelog.md
index 1f5de9f..169fa8a 100644
--- a/changelog.md
+++ b/changelog.md
@@ -4,3 +4,4 @@
 
 - Captured current implementation status, requirements coverage, missing features, and prioritized roadmap in `calminer-docs/implementation_status.md` to guide future development.
 - Added core SQLAlchemy domain models, shared metadata descriptors, and Alembic migration setup (with initial schema snapshot) to establish the persistence layer foundation.
+- Introduced repository and unit-of-work helpers for projects, scenarios, financial inputs, and simulation parameters to support service-layer operations.
diff --git a/services/exceptions.py b/services/exceptions.py
new file mode 100644
index 0000000..6e58c29
--- /dev/null
+++ b/services/exceptions.py
@@ -0,0 +1,9 @@
+"""Domain-level exceptions for service and repository layers."""
+
+
+class EntityNotFoundError(Exception):
+    """Raised when a requested entity cannot be located."""
+
+
+class EntityConflictError(Exception):
+    """Raised when attempting to create or update an entity that violates uniqueness."""
diff --git a/services/repositories.py b/services/repositories.py
new file mode 100644
index 0000000..bafff7b
--- /dev/null
+++ b/services/repositories.py
@@ -0,0 +1,146 @@
+from __future__ import annotations
+
+from collections.abc import Iterable
+from typing import Sequence
+
+from sqlalchemy import select
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.orm import Session, joinedload
+
+from models import FinancialInput, Project, Scenario, SimulationParameter
+from services.exceptions import EntityConflictError, EntityNotFoundError
+
+
+class ProjectRepository:
+    """Persistence operations for Project entities."""
+
+    def __init__(self, session: Session) -> None:
+        self.session = session
+
+    def list(self) -> Sequence[Project]:
+        stmt = select(Project).order_by(Project.created_at)
+        return self.session.execute(stmt).scalars().all()
+
+    def get(self, project_id: int, *, with_children: bool = False) -> Project:
+        stmt = select(Project).where(Project.id == project_id)
+        if with_children:
+            stmt = stmt.options(joinedload(Project.scenarios))
+        project = self.session.execute(stmt).scalar_one_or_none()
+        if project is None:
+            raise EntityNotFoundError(f"Project {project_id} not found")
+        return project
+
+    def create(self, project: Project) -> Project:
+        self.session.add(project)
+        try:
+            self.session.flush()
+        except IntegrityError as exc:  # pragma: no cover - reliance on DB constraints
+            raise EntityConflictError("Project violates uniqueness constraints") from exc
+        return project
+
+    def delete(self, project_id: int) -> None:
+        project = self.get(project_id)
+        self.session.delete(project)
+
+
+class ScenarioRepository:
+    """Persistence operations for Scenario entities."""
+
+    def __init__(self, session: Session) -> None:
+        self.session = session
+
+    def list_for_project(self, project_id: int) -> Sequence[Scenario]:
+        stmt = (
+            select(Scenario)
+            .where(Scenario.project_id == project_id)
+            .order_by(Scenario.created_at)
+        )
+        return self.session.execute(stmt).scalars().all()
+
+    def get(self, scenario_id: int, *, with_children: bool = False) -> Scenario:
+        stmt = select(Scenario).where(Scenario.id == scenario_id)
+        if with_children:
+            stmt = stmt.options(
+                joinedload(Scenario.financial_inputs),
+                joinedload(Scenario.simulation_parameters),
+            )
+        scenario = self.session.execute(stmt).scalar_one_or_none()
+        if scenario is None:
+            raise EntityNotFoundError(f"Scenario {scenario_id} not found")
+        return scenario
+
+    def create(self, scenario: Scenario) -> Scenario:
+        self.session.add(scenario)
+        try:
+            self.session.flush()
+        except IntegrityError as exc:  # pragma: no cover
+            raise EntityConflictError("Scenario violates constraints") from exc
+        return scenario
+
+    def delete(self, scenario_id: int) -> None:
+        scenario = self.get(scenario_id)
+        self.session.delete(scenario)
+
+
+class FinancialInputRepository:
+    """Persistence operations for FinancialInput entities."""
+
+    def __init__(self, session: Session) -> None:
+        self.session = session
+
+    def list_for_scenario(self, scenario_id: int) -> Sequence[FinancialInput]:
+        stmt = (
+            select(FinancialInput)
+            .where(FinancialInput.scenario_id == scenario_id)
+            .order_by(FinancialInput.created_at)
+        )
+        return self.session.execute(stmt).scalars().all()
+
+    def bulk_upsert(self, inputs: Iterable[FinancialInput]) -> Sequence[FinancialInput]:
+        entities = list(inputs)
+        self.session.add_all(entities)
+        try:
+            self.session.flush()
+        except IntegrityError as exc:  # pragma: no cover
+            raise EntityConflictError("Financial input violates constraints") from exc
+        return entities
+
+    def delete(self, input_id: int) -> None:
+        stmt = select(FinancialInput).where(FinancialInput.id == input_id)
+        entity = self.session.execute(stmt).scalar_one_or_none()
+        if entity is None:
+            raise EntityNotFoundError(f"Financial input {input_id} not found")
+        self.session.delete(entity)
+
+
+class SimulationParameterRepository:
+    """Persistence operations for SimulationParameter entities."""
+
+    def __init__(self, session: Session) -> None:
+        self.session = session
+
+    def list_for_scenario(self, scenario_id: int) -> Sequence[SimulationParameter]:
+        stmt = (
+            select(SimulationParameter)
+            .where(SimulationParameter.scenario_id == scenario_id)
+            .order_by(SimulationParameter.created_at)
+        )
+        return self.session.execute(stmt).scalars().all()
+
+    def bulk_upsert(
+        self, parameters: Iterable[SimulationParameter]
+    ) -> Sequence[SimulationParameter]:
+        entities = list(parameters)
+        self.session.add_all(entities)
+        try:
+            self.session.flush()
+        except IntegrityError as exc:  # pragma: no cover
+            raise EntityConflictError("Simulation parameter violates constraints") from exc
+        return entities
+
+    def delete(self, parameter_id: int) -> None:
+        stmt = select(SimulationParameter).where(SimulationParameter.id == parameter_id)
+        entity = self.session.execute(stmt).scalar_one_or_none()
+        if entity is None:
+            raise EntityNotFoundError(f"Simulation parameter {parameter_id} not found")
+        self.session.delete(entity)
diff --git a/services/unit_of_work.py b/services/unit_of_work.py
new file mode 100644
index 0000000..6bb8cb8
--- /dev/null
+++ b/services/unit_of_work.py
@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+from contextlib import AbstractContextManager
+from typing import Callable
+
+from sqlalchemy.orm import Session
+
+from config.database import SessionLocal
+from services.repositories import (
+    FinancialInputRepository,
+    ProjectRepository,
+    ScenarioRepository,
+    SimulationParameterRepository,
+)
+
+
+class UnitOfWork(AbstractContextManager["UnitOfWork"]):
+    """Simple unit-of-work wrapper around SQLAlchemy sessions."""
+
+    def __init__(self, session_factory: Callable[[], Session] = SessionLocal) -> None:
+        self._session_factory = session_factory
+        self.session: Session | None = None
+
+    def __enter__(self) -> "UnitOfWork":
+        self.session = self._session_factory()
+        self.projects = ProjectRepository(self.session)
+        self.scenarios = ScenarioRepository(self.session)
+        self.financial_inputs = FinancialInputRepository(self.session)
+        self.simulation_parameters = SimulationParameterRepository(self.session)
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback) -> None:
+        assert self.session is not None
+        if exc_type is None:
+            self.session.commit()
+        else:
+            self.session.rollback()
+        self.session.close()
+
+    def flush(self) -> None:
+        if not self.session:
+            raise RuntimeError("UnitOfWork session is not initialised")
+        self.session.flush()
+
+    def commit(self) -> None:
+        if not self.session:
+            raise RuntimeError("UnitOfWork session is not initialised")
+        self.session.commit()
+
+    def rollback(self) -> None:
+        if not self.session:
+            raise RuntimeError("UnitOfWork session is not initialised")
+        self.session.rollback()