Y Combinator (YC) is a prominent American technology startup accelerator and venture capital firm founded in March 2005 by Paul Graham, Jessica Livingston, Robert Tappan Morris, and Trevor Blackwell. Headquartered in San Francisco, California, YC has been instrumental in launching over 5,000 companies, including notable names like Airbnb, Coinbase, Cruise, DoorDash, Dropbox, Instacart, Reddit, Stripe, and Twitch. The accelerator operates two funding cycles annually, providing startups with seed money, mentorship, and resources to refine their business models and achieve product-market fit.

In January 2022, YC introduced a revised standard deal offering $500,000 in funding, comprising $125,000 for a 7% equity stake and an additional $375,000 via an uncapped SAFE note with a Most Favored Nation (MFN) clause. This structure aims to reduce fundraising stress for founders while benefiting YC and major venture firms. As of 2025, YC's portfolio companies have a combined valuation of $600 billion, reflecting its significant impact on the startup ecosystem.