Block Inc (formerly Square Inc) is an American multinational technology conglomerate founded in 2009 by Jack Dorsey and Jim McKelvey and launched its first platform in 2010. It has been traded as a public company on the New York Stock Exchange since November 2015 with the ticker symbol SQ.

From its founding to December 10, 2021, the company was named Square, Inc. The company's namesake product for small businesses is still titled "Square". Square is a payments platform aimed at small and medium businesses that allows them to accept credit card payments and use smartphone or tablet computers as payment registers for a point-of-sale system. Block has a number of other businesses. Cash App is a mobile app that allows monetary transfers both among users and between users and businesses. Afterpay is a buy-now-pay-later service. Weebly is a web hosting service. Tidal is a subscription-based music, podcast and video streaming service that offers audio and music videos.

The original inspiration for 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. Co-founders 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 readers.

In October 2020, Square put approximately 1% of their total assets ($50 million) in Bitcoin (4,709 bitcoins), citing Bitcoin's "potential to be a more ubiquitous currency in the future" as their 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 $500 million USD in 2021, around $190 million USD as of February 2023).

On March 2, 2021, Square reached an agreement to acquire majority ownership 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 currently own stock in Tidal, 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. However, on December 16, less than a week into the rebrand, H&R Block, sued the company for trademark infringement, claiming that the name seeks to confuse customers by misappropriating the Block brand name, which H&R owns.

On January 31, 2022, Block completed its acquisition of Afterpay.