Block, Inc. (formerly Square, Inc.) is an American technology company and financial services provider for consumers and merchants. Founded in 2009 by Jack Dorsey, it is the U.S. market leader in point-of-sale systems. As of 2024, Block has 57 million users and 4 million sellers, processing $241 billion in payments annually.

Block's inaugural product Square, launched in 2009, is a point-of-sale system. It allows sellers to accept card payments and manage operations, including bookings, e-commerce, inventory, payroll, banking, and obtaining business loans. Additionally, Block's portfolio includes Cash App, a consumer-focused digital wallet introduced in 2013. This app allows users to send, receive, save or borrow money, access a debit card, invest in stocks and bitcoin, and file taxes.

Block also owns Afterpay, a buy now, pay later business; Bitkey, a self-custody bitcoin wallet; Proto, a bitcoin mining system; and Tidal, a music streaming business.

The inspiration for Block's first product "Square" occurred to Jack Dorsey in 2009 when his friend Jim McKelvey was unable to complete a $2,000 sale of his glass faucets and fittings because he could not accept credit cards. Dorsey—who also co-founded Twitter—and McKelvey began developing the company out of a small office in St. Louis. The name "Square" derives from the company's square-shaped card reader product.

Square was designed to let small merchants accept card payments through a mobile device and a compact card reader, lowering the upfront cost and complexity traditionally associated with card acceptance.

According to Forbes, Block, then named Square, Inc., tested its payment method on 50,000 merchants in the summer of 2010, and was reporting a chargeback rate of less than 0.05 percent. In February 2011, Square was reportedly valued at approximately US$240 million, signing up 100,000 new merchants every month. In April 2011, Square announced that it had secured an investment from Visa. In October 2011, the company stated that it was processing about US$2 billion per year in payments through its "Square" card readers, charging 2.75 percent per swipe.

In 2012, Starbucks and Square announced a partnership that would allow Starbucks to use the Square payment technology to accept payments for coffee. In the same year, Starbucks also reportedly invested US$25 million in Square. Square was handling an annual payment volume of around US$6 billion around that time. In 2013, Square launched Cash App, a peer to peer payment service. In October 2014, the company launched a payroll feature within its Square payment processing system, following the additions of a merchant cash advance offering, a customer feedback product, and an invoicing service.

In 2015, Square stated that it processed about US$23.8 billion worth of payment volume in 2014. In the same year, the company sold shares in its initial public offering for US$9 per share, giving itself a market capitalization of $2.9 billion. In 2018, Vox reported Square as stating that over 7 million people used the Cash App in December 2017. Vox also stated that Cash App was the "No. 1 free finance app" in Apple's U.S. iPhone App Store and was "ahead" of PayPal and Venmo.

In October 2020, Square put approximately 1% of its total assets ($50 million) in Bitcoin (4,709 bitcoins), citing Bitcoin's "potential to be a more ubiquitous currency in the future" as its main reasoning. The company purchased approximately 3,318 bitcoins in February 2021 for a cost of around $170 million, bringing Square's total holdings to around 8,027 bitcoins (equivalent to around US$500 million in 2021, around US$481 million as of July 2024).

On March 2, 2021, Square reached an agreement to acquire majority ownership stake in Tidal. Square paid $297 million in cash and stock for Tidal, with Jay-Z joining the company's board of directors. Jay-Z, as well as other artists who owned stock in Tidal at the time, will remain stakeholders. On December 1, 2021, Square announced that it would change its company name to Block, Inc. on December 10. The change was announced shortly after Dorsey resigned as CEO of Twitter.

On December 10, 2021, the name change took effect, and Square, Inc. became Block, Inc. On December 16, less than a week into the rebrand, H&R Block sued the company for trademark infringement. The lawsuit claimed that the name sought to confuse customers by misappropriating the Block brand name owned by H&R Block. The lawsuit was resolved in April 2023 when the two companies jointly agreed to dismiss the suit. On January 31, 2022, Block completed its acquisition of Afterpay, an Australian buy now, pay later (BNPL) lender.