Y Combinator is a startup accelerator founded in March 2005 by Paul Graham, Jessica Livingston, Robert Tappan Morris and Trevor Blackwell. It invests in early stage companies in batches and ends each batch with a Demo Day for investors.
What it is
Companies apply, and selected founders join a batch of several months with office hours, guest talks and advice. The accelerator runs four batches a year. According to Wikipedia, its standard deal since January 2022 is 500,000 dollars, made of a post money SAFE for 7 percent and an uncapped SAFE with a most favored nation provision.
History
The program started in Cambridge, Massachusetts and Mountain View, California, and consolidated in Silicon Valley in January 2009. Sam Altman became president in 2014 and stepped down in 2019, followed by Geoff Ralston and, from January 2023, Garry Tan. In 2018 a software glitch accepted all 15,000 applicants before the error was reversed, and the summer 2022 intake was cut from 414 to 250 companies.
Wikipedia lists alumni such as Airbnb, Coinbase, Dropbox, DoorDash, Instacart, Stripe and Twitch, and reports more than 400 companies valued above 100 million dollars.
Why it matters to founders
Y Combinator shaped much of the startup playbook, from shipping a first version quickly to talking to users. Many entries in this encyclopedia, including Zapier, Stripe, Webflow and PostHog, went through it.
Related entries
See Paul Graham, Minimum viable product, Zapier and Stripe.
Y Combinator is part of Revenue and funding.
Sources
Wikipedia entry for Y Combinator. Reviewed October 2026.
