Abstract: Provided are computer implemented methods and systems for facilitating mobile device payments using barcodes displayed on mobile devices and scanned by merchants at checkout counters. When a customer is ready to tender a payment to a merchant, instead of using a credit card, cash, or check, the customer activates an application on his mobile device. The mobile device includes or obtains information about the payment system of this merchant. Furthermore, the mobile device includes or obtains information about the customer/mobile device user and then uses these two pieces of information to generate and display a barcode that encodes customer payment information specific to this merchant. The barcode is scanned at the checkout counter and processed to retrieve customer records from a database of the payment processing system. These records are then used to transfer funds between the merchant and customer, obtain discounts, and/or perform other retail transactions.