Cash App (formerly Square Cash) is a mobile payment service available in the United States and the United Kingdom that allows users to transfer money to one another (for a 1.5% fee for immediate transfer) using a mobile phone app. In September 2021, the service reported 70 million annual transacting users and US$1.8 billion in gross profit.

Cash App was launched by Block, Inc. (formerly Square, Inc. at its launch) in October 15, 2013 under the name "Square Cash".

In March 2015, Square introduced Square Cash for businesses. This allowed individuals, organizations, and business owners to create a unique username to send and receive money, known as a $cashtag. Since then, the $cashtag has become the most popular method for users to transfer money.

In January 2018, Cash App added support for bitcoin trading.

In October 2019, Cash App added support for stock trading to users in the United States.

In November 2020, Square announced it was acquiring Credit Karma Tax, a free do-it-yourself tax-filing service, for $50 million and would make it a part of its Cash App unit.

On November 3, 2021, Square opened Cash App to teenagers between 13 and 17. The app previously required its users to be at least 18 years old. Younger teens will need a parent or guardian to authorize their account and will not have access to cryptocurrency or stock trading until they turn 18. The service allows users to send, receive, and store money within the US and the UK (but not internationally). Users can transfer money out of Cash App to a bank account in their country. The Cash Card is a customizable debit card that allows users to spend their money at various retailers and withdraw cash from an ATM. When signing up for the Cash Card, users can customize it by selecting a color, adding stamps, drawing on it, and even making the card glow in the dark. Once your custom design is finalized, the card is sent to the user through the mail.

As of March 7, 2018, the Cash App supports automated clearing house (ACH) direct deposits. Cash App also does cash deposits under its "Paper Money" feature at participating retailers, where a retailer scans a bar code and deposits money for a nominal fee of $1 charged by Cash App.