A History of UNIX before Berkeley
- A detailed overview of Unix people and components, 1975-1984.
- http://www.darwinsys.com/history/hist.html

The Unix System: History and Timeline
- Historical summary and timeline.
- http://www.unix.org/what_is_unix/history_timeline.html

Unix History
- A detailed family tree.
- http://www.levenez.com/unix/

History of Unix, Linux, and Open Source
- Historical comparison of Unix and the free software movement.
- http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/history.html

About the FreeBSD Project
- History and overview from the FreeBSD Handbook.
- http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/history.html

OMU - One Man Unix
- Steve Hosgood's work with an early 1980s Unix clone. Includes some utility sources.
- http://rootprompt.org/article.php3?article=335

UNIX History Graphing Project
- Lists of release dates and dependencies for the various Unix flavors. A graphical representation of the Unix family tree is planned.
- http://minnie.tuhs.org/Unix_History/index.html

A Brief Synopsis of Unix History
- University of Indiana Knowledge Base article. Summary of Unix versions and links to related entries.
- http://kb.indiana.edu/data/acve.html?cust=7748

The UNIX Time-Sharing System
- Ritchie and Thompson's famous Communications of the ACM paper from 1974. An authoritative and technical overview of the operating system.
- http://cm.bell-labs.com/cm/cs/who/dmr/cacm.html

The Unix Heritage Society
- Built to foster the "the preservation and maintenance of historical and non-mainstream UNIX systems." Mailing list and archives. Includes early Unix source code, from 1973 through the 1990s.
- http://www.tuhs.org/

Unix Programmer's Manual, Seventh Edition
- Archives at Bell Labs of the 1979 manual. Troff source and formatted Gzipped PostScript/PDF versions.
- http://cm.bell-labs.com/7thEdMan/

Nick Moffitt's $7 History of Unix
- History paper detailing the people and places involved in developing Unix.
- http://crackmonkey.org/unix.html

Dennis Ritchie's Home Page
- Several historic technical reports, anecdotes, and stories from one of the fathers of Unix.
- http://plan9.bell-labs.com/cm/cs/who/dmr/

The Evolution of the Unix Time-Sharing System
- 1979 conference paper by Dennis Ritchie. "Concentrates on the evolution of the file system, the process-control mechanism, and the idea of pipelined commands. Some attention is paid to social conditions during the development of the system."
- http://cm.bell-labs.com/cm/cs/who/dmr/hist.html

History of the BSD Daemon
- Various drawings, pictures, and information on the red devil BSD mascot.
- http://www.mckusick.com/beastie/

CSRG Archive CD-ROMs
- The full source archives of the University of California at Berkeley's Computer Systems Research Group, for sale on a 4-CD set.
- http://www.mckusick.com/csrg/

Bell Labs: Selected Technical Reports
- Several classic Unix papers dating back to 1973. Most reports are Gzipped PostScript, some are in PDF.
- http://www.cs.bell-labs.com/cm/cs/cstr.html

A Brief History of Unix
- History of Unix and causes for its popularity. "This document is designed to give people with no previous UNIX experience some sense of what UNIX is. This document will cover the history of UNIX and an introduction to UNIX."
- http://www.hsrl.rutgers.edu/ug/unix_history.html