Y Combinator

Y Combinator is a startup accelerator based in California that invests a standard amount in each company it accepts and runs a roughly three-month program ending in a demo day where founders present to investors. Founded in 2005 by Paul Graham and his co-founders, it pioneered the batch model in which a cohort goes through the program together, receiving regular office hours, a structured focus on talking to users and growing weekly, and access to an alumni network that later supplies customers, hires, and follow-on funding. Airbnb, Stripe, Dropbox, Coinbase, and Instacart all came through it, which is why acceptance carries strong signaling value with investors. YC also publishes free material including Startup School and its Requests for Startups, and it operates Hacker News. Recent batches have skewed heavily toward AI companies, reflecting where founders and capital are concentrated. The standard caution is that the signal is not a guarantee. Most YC companies still fail, the accelerator takes equity at a very early stage that becomes expensive if the company succeeds, and the program's emphasis on rapid weekly growth suits consumer and SaaS businesses better than research-heavy or long-cycle hardware ventures.