Several outstanding books have been written about Icon and Unicon. Ordering these books, along with training, support, and consulting for Icon and Unicon are available from Jeffery Systems. Unicon research contracts are available through the University of Idaho.

The book, "Programming with Unicon", is the main definition of the language. It is updated periodically. You can look at it free online in PDF format; the book is freely copyable and modifiable under the terms of the GNU Free Documentation License. In order to make it more ``open'' in the 2nd edition, the Unicon book was converted to LaTex and its source is in the Unicon SVN repository (in doc/book/). There are some formatting tweaks and corrections/updates still needed. Please send us any bugs or comments you have to improve the book.
A forthcoming book, "The Implementation of Icon and Unicon: a Compendium", is in a draft stage. You can look at a draft manuscript preview in PDF format.
This book documents Icon extensions for high-level monitoring and visualization and includes numerous code examples. These facilities are enhanced in Unicon, which provides interpreters with and without monitoring, and doesn't require that you recompile your programs to switch from the regular interpreter to the monitoring interpreter. Published by Springer. At present, this book is out of print; a new edition is forthcoming which will cover extensions to the monitoring facilities for debugging. Errata
All the great graphics facilities developed for Icon are part of Unicon. "Graphics Programming in Icon" is available from Jeffery Systems. In addition, Robert Parlett has written a richer, better-designed, more extensible graphical user interface builder and class library, documented in "Programming with Unicon". A Unicon GUI primer is available in Unicon Technical Report #6.
Alan Corré has written the second edition of Icon Programming for Humanists, and generously made it available in an online format. The hard copies are published by Goal-Directed Press.