UNIX is 40 years old in August 2009. 

summary timeline:

1969 Ken Thompson at Bell Labs writes the first version of an operating system which is later called UNIX (named in 1970)

1971 first edition of the UNIX Programmer’s manual is written by Ken Thompson and Dennis Ritchie is published

1983 UNIX System V is launched and is the first supported release

2001 Version 3 of the Single UNIX Specification unites IEEE POSIX, The Open Group and the industry efforts. Linux 2.4 kernel released

2007 Apple Mac OS X certified to UNIX 03

for additional information: http://www.unix.org/what_is_unix/history_timeline.html