Paul Graham (b. Weymouth, England, 1964) is a Lisp programmer, venture capitalist, and essayist. He is the author of On Lisp (1993), ANSI Common Lisp (1995), and Hackers & Painters (2004).

In 1995 Graham and Robert Morris founded Viaweb, the first ASP. Viaweb's software, originally written mostly in Common Lisp, allowed users to make their own Internet stores. In the summer of 1998 Viaweb was sold to Yahoo! for 455,000 shares of Yahoo! stock, valued at $49.6 million.  At Yahoo! the product became Yahoo! Store..

He has since begun writing essays for his popular website paulgraham.com. They range from "Beating the Averages", which compares Lisp to other programming languages and introduced the word Blub, to "Why Nerds are Unpopular", a discussion of nerd life in high school. A collection of his essays has been published as Hackers and Painters (ISBN 0-596-00662-4) by O'Reilly.

In 2005, after giving a talk at the Harvard Computer Society later published as How to Start a Startup, Graham along with Trevor Blackwell, Jessica Livingston and Robert Morris started Y Combinator to provide seed funding to startups, particularly those started by younger, more technically-oriented founders. Y Combinator has now invested in 58 startups, including reddit, Justin.tv and loopt.

Graham has a B.A.  from Cornell. He earned an M.S. and a Ph.D. in Applied Sciences, (specializing in computer science) from Harvard in 1988 and 1990 respectively, and studied painting at Rhode Island School of Design and the Accademia di Belle Arti in Florence.

In 2001, Paul Graham announced that he was working on a new dialect of LISP named "Arc." Over the years since, he has written several essays describing features or goals of the language, and some internal projects at Y Combinator have been written in Arc, most notably the Hacker News web forum and news aggregator program.

In 2002, Graham published a an essay entitled "A Plan for Spam," in which he advocated using a Naive Bayes classifier to identify spam. This paper directly lead to the creation of the popular bogofilter software, which uses the method, and the inclusion of Bayesian Filtering in other existing products such as spamassassin.

Since "A Plan for Spam" Bayesian Filtering has come to be regarded as the best method for filtering spam in situations where the filter can be trained, beating older heuristic approaches both in terms of the simplicity of the process and the quality of the classification.