diff --git a/server/src/api/controllers/Contacts/Customers.ts b/server/src/api/controllers/Contacts/Customers.ts
index 14798b95d..382bf5982 100644
--- a/server/src/api/controllers/Contacts/Customers.ts
+++ b/server/src/api/controllers/Contacts/Customers.ts
@@ -32,6 +32,17 @@ export default class CustomersController extends ContactsController {
       asyncMiddleware(this.newCustomer.bind(this)),
       this.handlerServiceErrors
     );
+    router.post(
+      '/:id/opening_balance',
+      [
+        ...this.specificContactSchema,
+        check('opening_balance').exists().isNumeric().toFloat(),
+        check('opening_balance_at').optional().isISO8601(),
+      ],
+      this.validationResult,
+      asyncMiddleware(this.editOpeningBalanceCustomer.bind(this)),
+      this.handlerServiceErrors,
+    );
     router.post('/:id', [
       ...this.contactDTOSchema,
       ...this.contactEditDTOSchema,
@@ -160,6 +171,36 @@ export default class CustomersController extends ContactsController {
     }
   }
 
+  /**
+   * Changes the opening balance of the given customer.
+   * @param {Request} req -
+   * @param {Response} res -
+   * @param {NextFunction} next -
+   */
+  async editOpeningBalanceCustomer(req: Request, res: Response, next: NextFunction) {
+    const { tenantId } = req;
+    const { id: customerId } = req.params;
+    const {
+      openingBalance,
+      openingBalanceAt,
+    } = this.matchedBodyData(req);
+
+    try {
+      await this.customersService.changeOpeningBalance(
+        tenantId,
+        customerId,
+        openingBalance,
+        openingBalanceAt,
+      );
+      return res.status(200).send({
+        id: customerId,
+        message: 'The opening balance of the given customer has been changed successfully.',
+      });
+    } catch (error) {
+      next(error);
+    }
+  }
+
   /**
    * Deletes the given customer from the storage.
    * @param {Request} req 
@@ -283,6 +324,11 @@ export default class CustomersController extends ContactsController {
           errors: [{ type: 'CUSTOMER.HAS.SALES_INVOICES', code: 400 }],
         });
       }
+      if (error.errorType === 'OPENING_BALANCE_DATE_REQUIRED') {
+        return res.boom.badRequest(null, {
+          errors: [{ type: 'OPENING_BALANCE_DATE_REQUIRED', code: 500 }],
+        });
+      }
     }
     next(error);
   }
diff --git a/server/src/api/controllers/Contacts/Vendors.ts b/server/src/api/controllers/Contacts/Vendors.ts
index 162ac1c22..d8c80dee2 100644
--- a/server/src/api/controllers/Contacts/Vendors.ts
+++ b/server/src/api/controllers/Contacts/Vendors.ts
@@ -28,6 +28,17 @@ export default class VendorsController extends ContactsController {
       asyncMiddleware(this.newVendor.bind(this)),
       this.handlerServiceErrors,
     );
+    router.post(
+      '/:id/opening_balance',
+      [
+        ...this.specificContactSchema,
+        check('opening_balance').exists().isNumeric().toFloat(),
+        check('opening_balance_at').optional().isISO8601(),
+      ],
+      this.validationResult,
+      asyncMiddleware(this.editOpeningBalanceVendor.bind(this)),
+      this.handlerServiceErrors,
+    );
     router.post('/:id', [
       ...this.contactDTOSchema,
       ...this.contactEditDTOSchema,
@@ -144,6 +155,36 @@ export default class VendorsController extends ContactsController {
     }
   }
 
+  /**
+   * Changes the opening balance of the given vendor.
+   * @param {Request} req -
+   * @param {Response} res -
+   * @param {NextFunction} next -
+   */
+  async editOpeningBalanceVendor(req: Request, res: Response, next: NextFunction) {
+    const { tenantId } = req;
+    const { id: vendorId } = req.params;
+    const {
+      openingBalance,
+      openingBalanceAt,
+    } = this.matchedBodyData(req);
+
+    try {
+      await this.vendorsService.changeOpeningBalance(
+        tenantId,
+        vendorId,
+        openingBalance,
+        openingBalanceAt,
+      );
+      return res.status(200).send({
+        id: vendorId,
+        message: 'The opening balance of the given vendor has been changed successfully.',
+      });
+    } catch (error) {
+      next(error);
+    }
+  }
+
   /**
    * Deletes the given vendor from the storage.
    * @param {Request} req 
@@ -261,6 +302,11 @@ export default class VendorsController extends ContactsController {
           errors: [{ type: 'VENDOR.HAS.BILLS', code: 400 }],
         });
       }
+      if (error.errorType === 'OPENING_BALANCE_DATE_REQUIRED') {
+        return res.boom.badRequest(null, {
+          errors: [{ type: 'OPENING_BALANCE_DATE_REQUIRED', code: 500 }],
+        });
+      }
     }
     next(error);
   }
diff --git a/server/src/api/controllers/Expenses.ts b/server/src/api/controllers/Expenses.ts
index 46c343cb2..03789ea25 100644
--- a/server/src/api/controllers/Expenses.ts
+++ b/server/src/api/controllers/Expenses.ts
@@ -104,6 +104,7 @@ export default class ExpensesController extends BaseController {
       check('currency_code').optional().isString().isLength({ max: 3 }),
       check('exchange_rate').optional({ nullable: true }).isNumeric().toFloat(),
       check('publish').optional().isBoolean().toBoolean(),
+      check('payee_id').optional({ nullable: true }).isNumeric().toInt(),
 
       check('categories').exists().isArray({ min: 1 }),
       check('categories.*.index')
@@ -392,6 +393,11 @@ export default class ExpensesController extends BaseController {
           errors: [{ type: 'EXPENSE_ALREADY_PUBLISHED', code: 700 }],
         });
       }
+      if (error.errorType === 'contact_not_found') {
+        return res.boom.badRequest(null, {
+          errors: [{ type: 'CONTACT_NOT_FOUND', code: 800 }],
+        });
+      }
     }
     next(error);
   }
diff --git a/server/src/interfaces/Expenses.ts b/server/src/interfaces/Expenses.ts
index 4a3263f0f..8a7ebac76 100644
--- a/server/src/interfaces/Expenses.ts
+++ b/server/src/interfaces/Expenses.ts
@@ -22,7 +22,7 @@ export interface IExpense {
   publishedAt: Date|null,
   userId: number,
   paymentDate: Date,
-
+  payeeId: number,
   categories: IExpenseCategory[],
 }
 
@@ -43,7 +43,7 @@ export interface IExpenseDTO {
   publish: boolean,
   userId: number,
   paymentDate: Date,
-
+  payeeId: number,
   categories: IExpenseCategoryDTO[],
 }
 
diff --git a/server/src/repositories/EntityRepository.ts b/server/src/repositories/EntityRepository.ts
index 24898fe49..04fe9f421 100644
--- a/server/src/repositories/EntityRepository.ts
+++ b/server/src/repositories/EntityRepository.ts
@@ -205,14 +205,15 @@ export default class EntityRepository {
   }
 
   /**
-   * 
+   * Arbitrary relation graphs can be upserted (insert + update + delete)
+   * using the upsertGraph method.
    * @param graph 
    * @param options 
    */
   upsertGraph(graph, options) {
     // Keep the input grpah immutable
     const graphCloned = cloneDeep(graph);
-    return this.model.upsertGraph(graphCloned)
+    return this.model.query().upsertGraph(graphCloned, options)
   }
 
   /**
diff --git a/server/src/repositories/ExpenseRepository.ts b/server/src/repositories/ExpenseRepository.ts
index a93ad7e31..92ea4e8fc 100644
--- a/server/src/repositories/ExpenseRepository.ts
+++ b/server/src/repositories/ExpenseRepository.ts
@@ -1,6 +1,7 @@
 import TenantRepository from "./TenantRepository";
 import moment from "moment";
 import { Expense } from 'models';
+
 export default class ExpenseRepository extends TenantRepository {
   /**
    * Constructor method.
diff --git a/server/src/services/Contacts/ContactsService.ts b/server/src/services/Contacts/ContactsService.ts
index 97500d39a..6fc245f73 100644
--- a/server/src/services/Contacts/ContactsService.ts
+++ b/server/src/services/Contacts/ContactsService.ts
@@ -1,5 +1,6 @@
 import { Inject, Service } from 'typedi';
 import { difference, upperFirst, omit } from 'lodash';
+import moment from 'moment';
 import { ServiceError } from "exceptions";
 import TenancyService from 'services/Tenancy/TenancyService';
 import {
@@ -11,6 +12,10 @@ import JournalPoster from '../Accounting/JournalPoster';
 
 type TContactService = 'customer' | 'vendor';
 
+const ERRORS = {
+  OPENING_BALANCE_DATE_REQUIRED: 'OPENING_BALANCE_DATE_REQUIRED',
+};
+
 @Service()
 export default class ContactsService {
   @Inject()
@@ -26,13 +31,17 @@ export default class ContactsService {
    * @param {TContactService} contactService
    * @return {Promise<IContact>}
    */
-  public async getContactByIdOrThrowError(tenantId: number, contactId: number, contactService: TContactService) {
+  public async getContactByIdOrThrowError(
+    tenantId: number,
+    contactId: number,
+    contactService?: TContactService
+  ) {
     const { contactRepository } = this.tenancy.repositories(tenantId);
 
     this.logger.info('[contact] trying to validate contact existance.', { tenantId, contactId });
     const contact = await contactRepository.findOne({
       id: contactId,
-      contactService: contactService,
+      ...(contactService) && ({ contactService }),
     });
 
     if (!contact) {
@@ -185,4 +194,40 @@ export default class ContactsService {
       journal.deleteEntries(),
     ]);
   }
+
+  /**
+   * Chanages the opening balance of the given contact.
+   * @param {number} tenantId 
+   * @param {number} contactId
+   * @param {ICustomerChangeOpeningBalanceDTO} changeOpeningBalance 
+   * @return {Promise<void>}
+   */
+  public async changeOpeningBalance(
+    tenantId: number,
+    contactId: number,
+    contactService: string,
+    openingBalance: number,
+    openingBalanceAt?: Date|string,
+  ): Promise<void> {
+    const { contactRepository } = this.tenancy.repositories(tenantId);
+
+    // Retrieve the given contact details or throw not found service error.
+    const contact = await this.getContactByIdOrThrowError(tenantId, contactId, contactService);
+
+    // Should the opening balance date be required.
+    if (!contact.openingBalanceAt && !openingBalanceAt) {
+      throw new ServiceError(ERRORS.OPENING_BALANCE_DATE_REQUIRED);
+    };
+    // Changes the customer the opening balance and opening balance date.
+    await contactRepository.update({
+      openingBalance: openingBalance,
+
+      ...(openingBalanceAt) && ({
+        openingBalanceAt: moment(openingBalanceAt).toMySqlDateTime(),
+      }),
+    }, {
+      id: contactId,
+      contactService,
+    });
+  }
 }
\ No newline at end of file
diff --git a/server/src/services/Contacts/CustomersService.ts b/server/src/services/Contacts/CustomersService.ts
index 9ee8b30ed..43c2dd867 100644
--- a/server/src/services/Contacts/CustomersService.ts
+++ b/server/src/services/Contacts/CustomersService.ts
@@ -16,14 +16,13 @@ import {
   IContactNewDTO,
   IContactEditDTO,
   IContact,
-  ISaleInvoice
+  ISaleInvoice,
  } from 'interfaces';
 import { ServiceError } from 'exceptions';
 import TenancyService from 'services/Tenancy/TenancyService';
 import DynamicListingService from 'services/DynamicListing/DynamicListService';
 import events from 'subscribers/events';
 import moment from 'moment';
-import SaleInvoiceRepository from 'repositories/SaleInvoiceRepository';
 
 @Service()
 export default class CustomersService {
@@ -298,4 +297,31 @@ export default class CustomersService {
       throw new ServiceError('some_customers_have_invoices');
     }
   }
+
+  /**
+   * Changes the opening balance of the given customer.
+   * @param {number} tenantId 
+   * @param {number} customerId 
+   * @param {number} openingBalance 
+   * @param {string|Date} openingBalanceAt 
+   */
+  public async changeOpeningBalance(
+    tenantId: number,
+    customerId: number,
+    openingBalance: number,
+    openingBalanceAt: Date|string,
+  ) {
+
+    await this.contactService.changeOpeningBalance(
+      tenantId,
+      customerId,
+      'customer',
+      openingBalance,
+      openingBalanceAt,
+    );
+    // Triggers `onOpeingBalanceChanged` event.
+    await this.eventDispatcher.dispatch(events.customers.onOpeningBalanceChanged, {
+      tenantId, customerId, openingBalance, openingBalanceAt
+    });
+  }
 }
diff --git a/server/src/services/Contacts/VendorsService.ts b/server/src/services/Contacts/VendorsService.ts
index 16982d750..9c34ad725 100644
--- a/server/src/services/Contacts/VendorsService.ts
+++ b/server/src/services/Contacts/VendorsService.ts
@@ -251,4 +251,31 @@ export default class VendorsService {
       filterMeta: dynamicFilter.getResponseMeta(),
     };
   }
+
+  /**
+   * Changes the opeing balance of the given vendor.
+   * @param {number} tenantId 
+   * @param {number} vendorId 
+   * @param {number} openingBalance 
+   * @param {Date|string} openingBalanceAt 
+   */
+  public async changeOpeningBalance(
+    tenantId: number,
+    vendorId: number,
+    openingBalance: number,
+    openingBalanceAt: Date|string,
+  ): Promise<void> {
+
+    await this.contactService.changeOpeningBalance(
+      tenantId,
+      vendorId,
+      'vendor',
+      openingBalance,
+      openingBalanceAt,
+    );
+    // Triggers `onOpeingBalanceChanged` event.
+    await this.eventDispatcher.dispatch(events.vendors.onOpeningBalanceChanged, {
+      tenantId, vendorId, openingBalance, openingBalanceAt
+    });
+  }
 }
diff --git a/server/src/services/Expenses/ExpensesService.ts b/server/src/services/Expenses/ExpensesService.ts
index 27634afb5..c348bf227 100644
--- a/server/src/services/Expenses/ExpensesService.ts
+++ b/server/src/services/Expenses/ExpensesService.ts
@@ -12,6 +12,7 @@ import JournalCommands from 'services/Accounting/JournalCommands';
 import { IExpense, IExpensesFilter, IAccount, IExpenseDTO, IExpensesService, ISystemUser, IPaginationMeta } from 'interfaces';
 import DynamicListingService from 'services/DynamicListing/DynamicListService';
 import events from 'subscribers/events';
+import ContactsService from "services/Contacts/ContactsService";
 
 const ERRORS = {
   EXPENSE_NOT_FOUND: 'expense_not_found',
@@ -38,6 +39,9 @@ export default class ExpensesService implements IExpensesService {
   @EventDispatcher()
   eventDispatcher: EventDispatcherInterface;
 
+  @Inject()
+  contactsService: ContactsService;
+
   /**
    * Retrieve the payment account details or returns not found server error in case the 
    * given account not found on the storage.
@@ -323,6 +327,13 @@ export default class ExpensesService implements IExpensesService {
     // - Validate expenses accounts type.
     await this.validateExpensesAccountsType(tenantId, expensesAccounts);
 
+    // - Validate the expense payee contact id existance on storage.
+    if (expenseDTO.payeeId) {
+      await this.contactsService.getContactByIdOrThrowError(
+        tenantId,
+        expenseDTO.payeeId,
+      )
+    }
     // - Validate the given expense categories not equal zero.
     this.validateCategoriesNotEqualZero(expenseDTO);
 
@@ -346,8 +357,9 @@ export default class ExpensesService implements IExpensesService {
    * 2. Validate expense accounts exist on the storage.
    * 3. Validate payment account type.
    * 4. Validate expenses accounts type.
-   * 5. Validate the given expense categories not equal zero.
-   * 6. Stores the expense to the storage.
+   * 5. Validate the expense payee contact id existance on storage.
+   * 6. Validate the given expense categories not equal zero.
+   * 7. Stores the expense to the storage.
    * ---------
    * @param {number} tenantId 
    * @param {IExpenseDTO} expenseDTO 
@@ -359,26 +371,33 @@ export default class ExpensesService implements IExpensesService {
   ): Promise<IExpense> {
     const { expenseRepository } = this.tenancy.repositories(tenantId);
 
-    // 1. Validate payment account existance on the storage.
+    // - Validate payment account existance on the storage.
     const paymentAccount = await this.getPaymentAccountOrThrowError(
       tenantId,
       expenseDTO.paymentAccountId,
     );
-    // 2. Validate expense accounts exist on the storage.
+    // - Validate expense accounts exist on the storage.
     const expensesAccounts = await this.getExpensesAccountsOrThrowError(
       tenantId,
       this.mapExpensesAccountsIdsFromDTO(expenseDTO),
     );
-    // 3. Validate payment account type.
+    // - Validate payment account type.
     await this.validatePaymentAccountType(tenantId, paymentAccount);
 
-    // 4. Validate expenses accounts type.
+    // - Validate expenses accounts type.
     await this.validateExpensesAccountsType(tenantId, expensesAccounts);
 
-    // 5. Validate the given expense categories not equal zero.
+    // - Validate the expense payee contact id existance on storage.
+    if (expenseDTO.payeeId) {
+      await this.contactsService.getContactByIdOrThrowError(
+        tenantId,
+        expenseDTO.payeeId,
+      )
+    }
+    // - Validate the given expense categories not equal zero.
     this.validateCategoriesNotEqualZero(expenseDTO);
 
-    // 6. Save the expense to the storage.
+    // - Save the expense to the storage.
     const expenseObj = this.expenseDTOToModel(expenseDTO, authorizedUser);
     const expenseModel = await expenseRepository.upsertGraph(expenseObj);
 
diff --git a/server/src/services/Items/ItemsService.ts b/server/src/services/Items/ItemsService.ts
index b729e0d83..4e8394579 100644
--- a/server/src/services/Items/ItemsService.ts
+++ b/server/src/services/Items/ItemsService.ts
@@ -19,7 +19,7 @@ const ERRORS = {
 
   ITEMS_HAVE_ASSOCIATED_TRANSACTIONS: 'ITEMS_HAVE_ASSOCIATED_TRANSACTIONS',
   ITEM_HAS_ASSOCIATED_TRANSACTINS: 'ITEM_HAS_ASSOCIATED_TRANSACTINS'
-}
+};
 
 @Service()
 export default class ItemsService implements IItemsService {
diff --git a/server/src/subscribers/events.ts b/server/src/subscribers/events.ts
index 0bd55d059..10aa2f529 100644
--- a/server/src/subscribers/events.ts
+++ b/server/src/subscribers/events.ts
@@ -146,6 +146,7 @@ export default {
     onEdited: 'onCustomerEdited',
     onDeleted: 'onCustomerDeleted',
     onBulkDeleted: 'onBulkDeleted',
+    onOpeningBalanceChanged: 'onOpeingBalanceChanged',
   },
 
   /**
@@ -156,6 +157,7 @@ export default {
     onEdited: 'onVendorEdited',
     onDeleted: 'onVendorDeleted',
     onBulkDeleted: 'onVendorBulkDeleted',
+    onOpeningBalanceChanged: 'onOpeingBalanceChanged',
   },
 
   items: {