diff --git a/src/operations/category.service.ts b/src/operations/category.service.ts
new file mode 100644
index 0000000..675ff2d
--- /dev/null
+++ b/src/operations/category.service.ts
@@ -0,0 +1,22 @@
+// vim: set tw=80 ts=2 sw=2 sts=2:
+
+import { Injectable } from '@angular/core';
+import { Observable } from 'rxjs/Rx';
+
+import { Restangular } from "ngx-restangular";
+
+import { Category } from './category';
+
+@Injectable()
+export class CategoryService {
+  constructor(
+    private restangular: Restangular
+  ) {}
+
+  query(id: number, minDate: Date = null, maxDate: Date = null): Observable<Category[]> {
+    return this.restangular.one('account', id).getList('category', {
+      begin: minDate,
+      end: maxDate
+    });
+  }
+}
diff --git a/src/operations/category.ts b/src/operations/category.ts
new file mode 100644
index 0000000..fc7f2a6
--- /dev/null
+++ b/src/operations/category.ts
@@ -0,0 +1,7 @@
+// vim: set tw=80 ts=2 sw=2 sts=2 :
+
+export class Category {
+    category: string;
+    expenses: number;
+    revenues: number;
+}
diff --git a/src/operations/index.ts b/src/operations/index.ts
index c6eaa2a..ff56ea5 100644
--- a/src/operations/index.ts
+++ b/src/operations/index.ts
@@ -35,6 +35,7 @@ var categoryChartModule = require('./category-chart.component');
 import accountModule from '@accountant/accounts';
 
 import { BalanceChartComponent } from './balanceChart.component';
+import { CategoryService } from './category.service';
 
 var OperationFactory = require('./operation.factory');
 var OperationController = require('./operation.controller');
@@ -52,6 +53,8 @@ export default angular.module('accountant.operations', [
 
     .controller('OperationController', OperationController)
 
+    .factory('categoryService', downgradeInjectable(CategoryService))
+
     .directive('balanceChart', downgradeComponent({
         component: BalanceChartComponent
     }) as angular.IDirectiveFactory)
diff --git a/src/operations/operation.module.ts b/src/operations/operation.module.ts
index 76edc19..a646106 100644
--- a/src/operations/operation.module.ts
+++ b/src/operations/operation.module.ts
@@ -9,6 +9,7 @@ import { NgLoggerModule, Level } from '@nsalaun/ng-logger';
 import { RestangularModule } from 'ngx-restangular';
 
 import { BalanceChartComponent } from './balanceChart.component';
+import { CategoryService } from './category.service'
 
 @NgModule({
   imports: [
@@ -18,6 +19,9 @@ import { BalanceChartComponent } from './balanceChart.component';
     NgLoggerModule,
     RestangularModule,
   ],
+  providers: [
+    CategoryService,
+  ],
   declarations: [
     BalanceChartComponent,
   ],