Atlas Games
Atlas Games is the company that owns the Ars Magica franchise and publishes Ars Magica products. It has been publishing Ars Magica products since 1996 (see History of Ars Magica), including all of the Fourth and Fifth Edition. In addition to Ars Magica, Atlas Games also publishes other roleplaying games, as well as card games (the latter seem to be its main source of revenue).
See also the company webpage and the wikipedia entry.
Legacy Page
The history of this page before August 6, 2010 is archived at Legacy:atlas_games