Walmart customers can leave their cash and credit cards at home: The retailer today introduced its own mobile payment system.

Compatible with iOS and Android and major credit, debit, pre-paid, or Walmart gift cards, Walmart Pay is rolling out to select stores this month. A nationwide launch will be complete by the first half of 2016.

"Walmart Pay is the latest example … of how we are transforming the shopping experience by seamlessly connecting online, mobile and stores," Neil Ashe, CEO of Walmart Global eCommerce, said in a statement.

To sign up, tap the Walmart Pay section on the Walmart app. If you have multiple credit cards connected to your account, select the one you want to use for Walmart Pay, or opt to use a gift card. Create a four-digit passcode (or use Touch ID on iPhone) for security, accept the terms, and you're ready to go.

At Walmart, roll your cart up to any register, open the Walmart app, and tap Walmart Pay. The camera will activate, and you'll scan the code displayed at the register. An e-receipt will then be sent to the app.

Walmart Pay will integrate with other mobile wallets in the future, the company said, though it did not elaborate. Walmart is joining a crowded market, filled with products from Apple, Google, LG, Samsung, and MasterCard—which partnered with fashion designers and automakers to embed mobile payment technology into their products.