Guardians of the Forests
Guardians of the Forest: The Rhine Tribunal (often abbreviated to GotF) is a supplement for Ars Magica Fifth Edition released by Atlas Games in 2005. It details the canonic Rhine Tribunal. See also the product page.
Other Content
GotF introduces the concept of Journeyman on p. 20, to denote a magus not far past his gauntlet, as well as rules for becoming an Archmage on p. 24. In between it introduces the idea of a Master magus (p. 22-23), which is intended to be limited to the Rhine tribunal but seems to me to be applicable to many tribunals (although not all).
Information on Forest Path of power, a means to obtain virtues preceding the Mysteries version and involving the Forest Lore arcane ability, is given on p. 35-40. Note that this system was later expanded.
Rules for studying in the Great Library of Durenmar are on p. 55-57. Note that True Lineages expands on the contents, by including folios and the "tabula geographica magica" (a catalogue of magical magical sites and regiones; p. 13).
Specific books include a mention of "Principia Magica", the authority on Magic Theory written by Bonisagus (p. 57).
New Spells include several shortly-described ones on p. 60, and a new Mentem spell on p. 72.
The Order of Odin is briefly discussed on pages 112-113.
Legacy Page
The history of this page before August 6, 2010 is archived at Legacy:guardians_of_the_forest