420 is a favorite number for a variety of reasons, but colloquially the number says pot -- "let's smoke pot", or "someone's smoking pot", or "gee, i really like pot", or "time to smoke pot". It is celebrated and noted by time (4:20 a.m. or p.m.), date (April 20th), or in any other instance (e.g. State Route 420). April 20th at 4:20 is marked by annual events in Mount Tamalpais, CA (an informal gathering); Marin Conty, CA (the 420 Hemp Fest); Ann Arbor, MI (the Hash Bash); and Washington, D.C. (buildup towards the July 4th Smoke-In).

Related FAQ pages:

• Isnt' it police code?
• Why did it come to mean that?
• What are some other explanations of what it means?
• What does 420 have to do with Phish?
• Am I crazy, or is the number 420 everywhere recently?

See also:

• Much of the content from this section of the FAQ has been "borrowed" (reused without attribution, or permission, but hey...) for an article on Wikipedia, and there somewhat improved upon and extended
• Groups including Inside Out (an effort to curb the hard drug scourge) and The Phellowship (for folks who want support seeing Phish shows sober)
• Verbage including other slang for hemp.
• Plus the Amsterdam weather forecast, the 420 Song ( RealPlayer exerpt) Bobby G from 1966, and Cheech and Chong.

Thanks also to Jonathan Fox, Alfred Hall, and John Simons.