The user documentation for the different versions can be found here:

* [[6.9.0|http://ftp.x.org/pub/X11R6.9.0/doc/html]]
* [[7.0|http://ftp.x.org/pub/X11R7.0/doc/html]]
* [[7.5|http://www.x.org/releases/X11R7.5/doc/]]
* [[7.6|http://www.x.org/releases/X11R7.6/doc/]]
* [[7.7|http://www.x.org/releases/X11R7.7/doc/]]

A brief getting started guide and tutorial for end-users and non-programmers is [[here|UserDocumentation/GettingStarted]].

O'Reilly & Associates have also made freely available online some of their classic X Window System manuals. These are a bit older, dating from the [[X11R3|X11R3]], [[R4|X11R4]], or [[R5|X11R5]] eras, and applying to the commercial Unix versions of the time, but may still have some useful information in:

* [[X Series Volume 3: X Window System User's Guide, 3rd Edition (1990, covers X11R3 & R4)|http://www.archive.org/details/xwindowsystem03quermiss]]
* [[X Series Volume 3: X Window System User's Guide, OSF/Motif Edition (1990, covers X11R4 & Motif 1.1)|http://www.archive.org/details/xwindowsytemosf03querarch]]
* [[X Series Volume 3: X Window System User's Guide, OpenLook Edition (never published)|http://www.oreilly.com/openbook/openlook/]]
* [[X Series Volume 8: X Window System Administrator's Guide, 1st edition (1993, covers X11R5)|http://www.archive.org/details/xwindowsystemadm08muimiss]]

O'Reilly has published a much more recent and up-to-date user guide [[X Power Tools|http://books.google.com/books?id=V1ZBeNJIx7UC]], but only a small preview of it is available for free online at this point.