Paul Graham launched Y Combinator in Cambridge, Massachusetts, in 2005.
Y Combinator was created to provide seed funding, mentorship and a structured program for early-stage startups. Its first batch included just eight companies, and the accelerator initially operated from Cambridge before moving to Silicon Valley.
Y Combinator became known for investing a small amount of money in each startup in exchange for equity, then bringing founders together for advice and a final investor presentation known as Demo Day. Its alumni include Airbnb, Dropbox, Stripe and Reddit.
Y Combinator is sometimes confused with Techstars or 500 Global, which are separate accelerator networks founded later. Paul Graham co-founded Y Combinator with Jessica Livingston, Robert Morris and Trevor Blackwell.