Casus Belli is a French roleplaying and wargaming magazine first published in 1980.
Initial print runs of the quarterly, then bi-monthly 32-page black and white magazine, were for only 2,000 pieces. (The pagecount varied among different eras and publishers, and the magazine featured color later on.)
After 122 issues it ceased production in 1999 following the general decline of the roleplaying and wargaming market and in the face of competition from the internet; it was said the magazine was produced at a loss in the end.
Arkana Press took over the established magazine for a second incarnation from 2000 on, implementing major changes. They sold it on in 2006, after 39 issues.
A new publisher, Casus Belli Press, restarted publication in 2010 but folded again in early 2011 due to financial difficulties. Then a fourth incarnation soldiered on until at least 2013.
Casus Belli had close ties (at least for a time) to Jeux Descartes, who held the license for the French edition of BattleTech, in the sense of a house magazine. As such, its BattleTech-related content can arguably be regarded as apocryphal, at least for the time when it was published under Jeux Descartes' aegis.