diff --git a/internal/domain/order.go b/internal/domain/order.go
new file mode 100644
index 0000000..23fc535
--- /dev/null
+++ b/internal/domain/order.go
@@ -0,0 +1,32 @@
+package domain
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+var (
+	ErrOrderAlreadyExist = errors.New("order already exist")
+	ErrOrderNotFound     = errors.New("order not found")
+	ErrInvalidOrderData  = errors.New("invalid order data")
+)
+
+type Order struct {
+	ID       string
+	Item     string
+	Quantity int32
+}
+
+func (o *Order) Validate() error {
+	if strings.TrimSpace(o.Item) == "" {
+		return fmt.Errorf("%w: item cannot be empty", ErrInvalidOrderData)
+	}
+	if o.Quantity <= 0 {
+		return fmt.Errorf("%w: quantity must be positive", ErrInvalidOrderData)
+	}
+	if o.ID == "" {
+		return fmt.Errorf("%w: ID cannot be empty", ErrInvalidOrderData)
+	}
+	return nil
+}
diff --git a/internal/handler/grpc/errors.go b/internal/handler/grpc/errors.go
new file mode 100644
index 0000000..aa7ae1e
--- /dev/null
+++ b/internal/handler/grpc/errors.go
@@ -0,0 +1,24 @@
+package handler
+
+import (
+	"errors"
+
+	"orderservice/internal/domain"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+func mapError(err error) error {
+	if errors.Is(err, domain.ErrOrderNotFound) {
+		return status.Error(codes.NotFound, err.Error())
+	}
+	if errors.Is(err, domain.ErrOrderAlreadyExist) {
+		return status.Error(codes.AlreadyExists, err.Error())
+	}
+	if errors.Is(err, domain.ErrInvalidOrderData) {
+		return status.Error(codes.InvalidArgument, err.Error())
+	}
+
+	return status.Error(codes.Internal, "internal server error")
+}
diff --git a/internal/handler/grpc/order.go b/internal/handler/grpc/order.go
new file mode 100644
index 0000000..53e3fb0
--- /dev/null
+++ b/internal/handler/grpc/order.go
@@ -0,0 +1,91 @@
+package handler
+
+import (
+	"context"
+
+	"orderservice/internal/domain"
+	"orderservice/internal/service"
+	pb "orderservice/pkg/api/order"
+)
+
+type OrderHandler struct {
+	pb.UnimplementedOrderServiceServer
+
+	service *service.OrderService
+}
+
+func NewOrderHandler(service *service.OrderService) *OrderHandler {
+	return &OrderHandler{
+		service: service,
+	}
+}
+
+func mapDomainStructToHandler(order *domain.Order) *pb.Order {
+	return &pb.Order{
+		Id:       order.ID,
+		Item:     order.Item,
+		Quantity: order.Quantity,
+	}
+}
+
+func (h *OrderHandler) CreateOrder(
+	ctx context.Context,
+	req *pb.CreateOrderRequest,
+) (*pb.CreateOrderResponse, error) {
+	order, err := h.service.Create(ctx, req.GetItem(), req.GetQuantity())
+	if err != nil {
+		return nil, mapError(err)
+	}
+
+	return &pb.CreateOrderResponse{Id: order.ID}, nil
+}
+
+func (h *OrderHandler) GetOrder(ctx context.Context, req *pb.GetOrderRequest) (*pb.GetOrderResponse, error) {
+	order, err := h.service.Get(ctx, req.GetId())
+	if err != nil {
+		return nil, mapError(err)
+	}
+
+	return &pb.GetOrderResponse{Order: mapDomainStructToHandler(order)}, nil
+}
+
+func (h *OrderHandler) UpdateOrder(
+	ctx context.Context,
+	req *pb.UpdateOrderRequest,
+) (*pb.UpdateOrderResponse, error) {
+	order, err := h.service.Update(ctx, req.GetId(), req.GetItem(), req.GetQuantity())
+	if err != nil {
+		return nil, mapError(err)
+	}
+
+	return &pb.UpdateOrderResponse{Order: mapDomainStructToHandler(order)}, nil
+}
+
+func (h *OrderHandler) DeleteOrder(
+	ctx context.Context,
+	req *pb.DeleteOrderRequest,
+) (*pb.DeleteOrderResponse, error) {
+	err := h.service.Delete(ctx, req.GetId())
+	if err != nil {
+		return nil, mapError(err)
+	}
+
+	return &pb.DeleteOrderResponse{Success: true}, nil
+}
+
+func (h *OrderHandler) ListOrders(
+	ctx context.Context,
+	_ *pb.ListOrdersRequest,
+) (*pb.ListOrdersResponse, error) {
+	domainOrders, err := h.service.List(ctx)
+	if err != nil {
+		return nil, mapError(err)
+	}
+
+	orders := make([]*pb.Order, 0, len(domainOrders))
+	for _, o := range domainOrders {
+		orders = append(orders, mapDomainStructToHandler(o))
+	}
+
+	return &pb.ListOrdersResponse{Orders: orders}, nil
+}
diff --git a/internal/repository/inmemory/order.go b/internal/repository/inmemory/order.go
new file mode 100644
index 0000000..f3da9e2
--- /dev/null
+++ b/internal/repository/inmemory/order.go
@@ -0,0 +1,100 @@
+package inmemory
+
+import (
+	"context"
+	"sync"
+
+	"orderservice/internal/domain"
+)
+
+type OrderRepository struct {
+	mu     sync.RWMutex
+	orders map[string]*domain.Order
+}
+
+func NewOrderRepository() *OrderRepository {
+	return &OrderRepository{
+		orders: make(map[string]*domain.Order),
+	}
+}
+
+func (r *OrderRepository) Create(ctx context.Context, order *domain.Order) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if _, ok := r.orders[order.ID]; ok {
+		return domain.ErrOrderAlreadyExist
+	}
+	r.orders[order.ID] = order
+
+	return nil
+}
+
+func (r *OrderRepository) Get(ctx context.Context, id string) (*domain.Order, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
+	order, ok := r.orders[id]
+	if !ok {
+		return nil, domain.ErrOrderNotFound
+	}
+
+	return order, nil
+}
+
+func (r *OrderRepository) Update(ctx context.Context, order *domain.Order) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if _, ok := r.orders[order.ID]; !ok {
+		return domain.ErrOrderNotFound
+	}
+	r.orders[order.ID] = order
+
+	return nil
+}
+
+func (r *OrderRepository) Delete(ctx context.Context, id string) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if _, ok := r.orders[id]; !ok {
+		return domain.ErrOrderNotFound
+	}
+
+	delete(r.orders, id)
+
+	return nil
+}
+
+func (r *OrderRepository) List(ctx context.Context) ([]*domain.Order, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
+	orders := make([]*domain.Order, 0, len(r.orders))
+	for _, order := range r.orders {
+		orders = append(orders, order)
+	}
+
+	return orders, nil
+}
diff --git a/internal/repository/order.go b/internal/repository/order.go
new file mode 100644
index 0000000..48f0459
--- /dev/null
+++ b/internal/repository/order.go
@@ -0,0 +1,15 @@
+package repository
+
+import (
+	"context"
+
+	"orderservice/internal/domain"
+)
+
+type OrderRepository interface {
+	Create(ctx context.Context, order *domain.Order) error
+	Get(ctx context.Context, id string) (*domain.Order, error)
+	Update(ctx context.Context, order *domain.Order) error
+	Delete(ctx context.Context, id string) error
+	List(ctx context.Context) ([]*domain.Order, error)
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index 1a57181..904597b 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -7,6 +7,9 @@ import (
 
 	"orderservice/internal/config"
 	"orderservice/internal/interceptor"
+
+	orderGrpcHandler "orderservice/internal/handler/grpc"
+	orderInMemory "orderservice/internal/repository/inmemory"
 	"orderservice/internal/service"
 
 	pb "orderservice/pkg/api/order"
@@ -35,8 +38,11 @@ func New(cfg *config.Config) *Server {
 }
 
 func (s *Server) RegisterServices() {
-	orderService := service.NewOrderServiceServer()
-	pb.RegisterOrderServiceServer(s.grpcServer, orderService)
+	repo := orderInMemory.NewOrderRepository()
+	orderService := service.NewOrderService(repo)
+	orderHandler := orderGrpcHandler.NewOrderHandler(orderService)
+
+	pb.RegisterOrderServiceServer(s.grpcServer, orderHandler)
 
 	if s.config.GRPCEnableReflection {
 		reflection.Register(s.grpcServer)
diff --git a/internal/service/order.go b/internal/service/order.go
new file mode 100644
index 0000000..10dede4
--- /dev/null
+++ b/internal/service/order.go
@@ -0,0 +1,70 @@
+package service
+
+import (
+	"context"
+
+	"orderservice/internal/domain"
+	"orderservice/internal/repository"
+
+	"github.com/google/uuid"
+)
+
+type OrderService struct {
+	repo repository.OrderRepository
+}
+
+func NewOrderService(repo repository.OrderRepository) *OrderService {
+	return &OrderService{
+		repo: repo,
+	}
+}
+
+func (s *OrderService) Create(ctx context.Context, item string, quantity int32) (*domain.Order, error) {
+	order := &domain.Order{
+		ID:       uuid.NewString(),
+		Item:     item,
+		Quantity: quantity,
+	}
+
+	err := order.Validate()
+	if err != nil {
+		return nil, err
+	}
+
+	if err := s.repo.Create(ctx, order); err != nil {
+		return nil, err
+	}
+	return order, nil
+}
+
+func (s *OrderService) Get(ctx context.Context, id string) (*domain.Order, error) {
+	return s.repo.Get(ctx, id)
+}
+
+func (s *OrderService) Update(ctx context.Context, id string, item string, quantity int32) (*domain.Order, error) {
+	order, err := s.repo.Get(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+
+	order.Item = item
+	order.Quantity = quantity
+
+	err = order.Validate()
+	if err != nil {
+		return nil, err
+	}
+
+	if err := s.repo.Update(ctx, order); err != nil {
+		return nil, err
+	}
+	return order, nil
+}
+
+func (s *OrderService) Delete(ctx context.Context, id string) error {
+	return s.repo.Delete(ctx, id)
+}
+
+func (s *OrderService) List(ctx context.Context) ([]*domain.Order, error) {
+	return s.repo.List(ctx)
+}
diff --git a/internal/service/order_service.go b/internal/service/order_service.go
deleted file mode 100644
index 37d49eb..0000000
--- a/internal/service/order_service.go
+++ /dev/null
@@ -1,110 +0,0 @@
-package service
-
-import (
-	"context"
-	"errors"
-	"sync"
-
-	pb "orderservice/pkg/api/order"
-
-	"github.com/google/uuid"
-)
-
-var ErrOrderNotFound = errors.New("order not found")
-
-func generateOrderID() string {
-	return uuid.NewString()
-}
-
-type OrderServiceServer struct {
-	pb.UnimplementedOrderServiceServer
-
-	mu     sync.RWMutex
-	orders map[string]*pb.Order
-}
-
-func NewOrderServiceServer() *OrderServiceServer {
-	return &OrderServiceServer{
-		orders: make(map[string]*pb.Order),
-	}
-}
-
-func (s *OrderServiceServer) CreateOrder(
-	_ context.Context,
-	req *pb.CreateOrderRequest,
-) (*pb.CreateOrderResponse, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-
-	id := generateOrderID()
-	order := &pb.Order{
-		Id:       id,
-		Item:     req.GetItem(),
-		Quantity: req.GetQuantity(),
-	}
-	s.orders[id] = order
-
-	return &pb.CreateOrderResponse{Id: id}, nil
-}
-
-func (s *OrderServiceServer) GetOrder(_ context.Context, req *pb.GetOrderRequest) (*pb.GetOrderResponse, error) {
-	s.mu.RLock()
-	defer s.mu.RUnlock()
-
-	order, ok := s.orders[req.GetId()]
-	if !ok {
-		return nil, ErrOrderNotFound
-	}
-
-	return &pb.GetOrderResponse{Order: order}, nil
-}
-
-func (s *OrderServiceServer) UpdateOrder(
-	_ context.Context,
-	req *pb.UpdateOrderRequest,
-) (*pb.UpdateOrderResponse, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-
-	order, ok := s.orders[req.GetId()]
-	if !ok {
-		return nil, ErrOrderNotFound
-	}
-
-	order.Item = req.GetItem()
-	order.Quantity = req.GetQuantity()
-
-	return &pb.UpdateOrderResponse{Order: order}, nil
-}
-
-func (s *OrderServiceServer) DeleteOrder(
-	_ context.Context,
-	req *pb.DeleteOrderRequest,
-) (*pb.DeleteOrderResponse, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-
-	_, ok := s.orders[req.GetId()]
-	if !ok {
-		return nil, ErrOrderNotFound
-	}
-
-	delete(s.orders, req.GetId())
-
-	return &pb.DeleteOrderResponse{Success: true}, nil
-}
-
-func (s *OrderServiceServer) ListOrders(
-	_ context.Context,
-	_ *pb.ListOrdersRequest,
-) (*pb.ListOrdersResponse, error) {
-	s.mu.RLock()
-	defer s.mu.RUnlock()
-
-	orders := make([]*pb.Order, 0, len(s.orders))
-	for _, o := range s.orders {
-		orders = append(orders, o)
-	}
-
-	return &pb.ListOrdersResponse{Orders: orders}, nil
-}