Y Combinator
Y Combinator (YC) is an American startup accelerator and venture capital firm based in San Francisco, California. Founded in March 2005 by Paul Graham, Jessica Livingston, Robert Morris, and Trevor Blackwell, it has funded more than 5,000 companies with a combined valuation exceeding $600 billion.41 Notable alumni include Airbnb, Stripe, Dropbox, Reddit, Coinbase, DoorDash, Instacart, and OpenAI.1
Founding
Graham conceived Y Combinator after selling his startup Viaweb to Yahoo in 1998 for $49 million and writing a series of essays on startups.2 The initial idea was to fund companies "synchronously" in batches, rather than one at a time — compressing the learning curve and letting founders support each other through the same gauntlet simultaneously.2 Graham, Livingston, Morris, and Blackwell launched the first batch in Cambridge, Massachusetts, in the summer of 2005 with eight companies, each receiving around $6,000 per founder.12
Livingston played a central role in the firm's day-to-day operations and founder selection, though early accounts often overlooked her contribution.1 The program ran in both Cambridge and Mountain View until January 2009, when YC consolidated operations fully in Silicon Valley.1
The accelerator model
YC runs multiple batches per year, each lasting roughly three months.1 The current standard deal provides $500,000 in seed funding: $125,000 on a post-money SAFE for 7% equity, plus $375,000 on an uncapped SAFE with a most favored nation (MFN) provision.1 Non-profits receive a $100,000 donation.1
The program centers on weekly group meetings, one-on-one office hours with partners, and culminates in Demo Day, where companies present to an audience of investors.1 YC takes no board seats and does not require a lead investor; the theory is that peer pressure from batchmates and frequent partner interaction compresses years of learning into months.3
The model has been widely imitated. Techstars, 500 Startups, and dozens of regional accelerators across the world follow the batch-mentorship-demo day structure that YC pioneered.3
Application and selection
Over 10,000 companies apply each batch, of which roughly 1% — typically 250–300 — are accepted.118 The Winter 2024 batch was described as "one of the most selective cohorts in YC history," with an acceptance rate below 1%.8 The Summer 2024 batch acceptance rate fell as low as 0.6%.10
The application consists of short written answers (the most famous: "What are you building and why?") followed by a 10-minute in-person or video interview with YC partners.10 The brevity is intentional — YC bets on founders, not business plans, and the interview is designed to surface conviction and clarity of thinking over polish.3
In August 2024, YC announced its first-ever Fall batch, breaking from the Winter/Summer cadence it had maintained since 2005.9
Philosophy and the essay canon
Much of YC's outsized cultural influence derives not from its capital but from Paul Graham's essays, which have become foundational reading for a generation of founders. Written mostly between 2004 and 2016, the essays articulate a coherent theory of startups: that the best founders are technically gifted hackers who have learned to understand what people want.2
Key texts that shaped startup culture:
| Essay | Core idea |
|---|---|
| Do Things That Don't Scale (2013) | Early-stage startups should do manually what they hope to automate; recruit users one at a time, obsess over early customers7 |
| Startups = Growth (2012) | A startup is a company designed to grow fast; growth rate is the single defining metric1 |
| How to Get Startup Ideas (2012) | The best ideas come from noticing problems you personally have, not from brainstorming1 |
| Default Alive or Default Dead (2015) | Every startup should know whether it will reach profitability before running out of money1 |
The phrase "make something people want" — the YC motto — originates from Graham's writing and is printed on the walls of YC's offices.3
Hacker News
Hacker News (HN) launched on February 19, 2007, as a side project to test Graham's Arc programming language — a Lisp dialect he had spent years developing.6 The original pitch was a link aggregator for "hackers" in the original sense: curious, technically-minded people who build things. Graham initially imagined it as a watering hole for current and future YC founders.6
HN grew well beyond that scope. By the early 2010s it had become one of the primary venues where developers, founders, and researchers shared links and debated ideas. Its voting and comment moderation system — built entirely in Arc, later migrated to Common Lisp — became a subject of study in its own right.6 The site's culture prizes intellectual curiosity over controversy, and its moderation philosophy (be substantive, disagree politely, no snark) has been more influential than most explicit community guidelines.
YC jobs postings on HN have become a reliable signal of hiring activity across the startup ecosystem, and an "Ask HN" post can generate more substantive expert discussion than most industry conferences.
Fund history
In 2009, Sequoia Capital led a $2 million investment in YC, enabling the accelerator to fund around 60 companies per year.1 Sequoia followed with an $8.25 million round in 2010.1 In 2011, Yuri Milner and SV Angel offered every YC company a $150,000 convertible note, which was later reduced to $80,000 when the Start Fund was renewed.1
When Sam Altman became president in 2014, he revised the standard deal to $150,000 for 7% equity.1 In January 2022, YC increased the deal to $500,000, split between a $125,000 post-money SAFE (7% equity) and a $375,000 uncapped SAFE with MFN.1
YC operated a Continuity Fund for pro-rata investments in alumni companies, but shut it down in March 2023 under Garry Tan's leadership.1
Leadership
Sam Altman was a member of YC's inaugural 2005 batch as a founder (of Loopt). Graham appointed him president in 2014.1 Altman stepped back in 2019 to focus on OpenAI, and Geoff Ralston succeeded him.1 In January 2023, Garry Tan (YC W08) became president and CEO.1 Michael Seibel served as managing director before stepping down in March 2024; Jared Friedman succeeded him.1
In 2010, Alexis Ohanian and Harj Taggar joined as advisors; Paul Buchheit (creator of Gmail) and Taggar were named partners later that year.1 Peter Thiel served as a visiting partner from 2015 to 2017.1
Notable portfolio companies
As of 2025, YC has funded over 5,000 companies.4 Its most successful investments by valuation include:
| Era | Companies |
|---|---|
| 2005–2009 | Reddit, Loopt, Justin.tv (later Twitch), Disqus |
| 2010–2014 | Dropbox (S07), Airbnb (W09), Stripe (S09), Instacart |
| 2015–2019 | Coinbase (S12), DoorDash (S13), Scale AI (S16), Helion Energy (S17) |
| 2020–2026 | Brex, Deel, Starcloud (fastest YC unicorn — 17 months post-demo day) |
Altman co-founded OpenAI in 2015 as a project within YC Research, with initial funding from Altman, Elon Musk, and others.1 OpenAI later spun off as an independent entity and is now among the most valuable private companies in the world.
YC Research and spin-offs
In October 2015, Altman launched YC Research, funding long-term fundamental research with a $10 million personal donation.1 OpenAI was its first project.1 A basic income study and a "new cities" research project followed.1 The Human Advancement Research Community (HARC), which counted Alan Kay and Bret Victor among its members, operated from 2016 until its shutdown in 2017.1 YC Research disaffiliated from YC and was renamed Open Research in 2020.1
International expansion
YC launched a China program in 2018 under Qi Lu, a former Baidu and Microsoft executive.1 Lu departed in November 2018 and YC decided not to continue the program.1 The effort later morphed into MiraclePlus, an independent accelerator led by Lu.1
In 2016, YC partners visited 11 countries (including Nigeria, India, and Israel) to engage with international founder communities.1 In June 2025, YC held its first AI Startup School in San Francisco, with speakers including Elon Musk, Sam Altman, Satya Nadella, and Andrej Karpathy.1
Startup School
YC launched Startup School in 2017 as a free online course for aspiring founders.1 Over 1,500 startups graduated from the program in its first year.1 In 2018, a software glitch initially accepted all 15,000 applicants before rejecting them hours later. After backlash, YC admitted all 15,000 companies.1
Controversies
Altman's departure from YC to focus on OpenAI drew scrutiny in 2023 when OpenAI's board briefly fired him. Reports emerged that Altman had been pushed out of the YC presidency in 2019 over conflicts of interest, rather than leaving voluntarily as had been publicly portrayed.1
In 2022, YC deliberately reduced its batch size by 40%, from 414 companies to approximately 250, citing quality concerns.1 The firm has also faced criticism for the equity stakes it takes (7% for $125,000 of the standard deal), which some founders argue represents expensive capital relative to what early-stage companies receive in return.5
In 2019, YC moved its headquarters from Mountain View to San Francisco, reflecting the city's growing concentration of AI companies and YC's increasing focus on the sector.1