Ars Magica is a role-playing game set in Mythic Europe, an idealized (or quasi-historical) version of Europe around 1200 AD. The game revolves around magic-using wizards and their allies. The game was originally developed by Jonathan Tweet and Mark Rein-Hagen in the late 1980s.

Player characters take on the role of either Wizards (Magi; singular: Magus (male), Maga (female)) or Companions (Consortes, singular Consors). Additionally, there are Grogs (menial workers) played/controled by all characters. The wizards live clustered in specific citadels (called Covenants), which are often built in places of power. (Covenants are the home base for the Magi, but they tend to roam the Magical Europe for their adventures.) Companions are select skilled non-magi (warriors, foresters, merchants, hermits, knights, castellan, and so forth) who help wizards conduct their affairs (Magi tend to be distanced from "normals" due to their study of magic). In addition to the "authentic" feel from having such a historical setting, the game uses medieval Latin for a number of key terms..

In the game process player characters are battling various creatures from the four main parallel worlds: celestial Angels, infernal Demons, magical beings (such as Dragons and Chimeras) & Faerie beings, in addition to dealing with the Medieval Church (which can be Antagonisit (Inquisition/Witchfinders), or merely Disaproving), and other Magi (Hermetic/Covenent or "Hedge-wizards").

The game system is rather inovative, with everything based on d10. The heart of the game is the magic system, and is the most celebrated and emulated magic system in the Role-Playing Games World. There are 15 "Arts" divided into 5 "Techniques" & 10 "Forms". The Techniques are what one DOES (actions); the Forms are what one does it TO or WITH (objects); this is sometimes called a "Verb/Noun" magic-system. Spell-casting is the act of combining a Technique & a Form under the will of the wizard. The Arts are named in Latin; the Techniques are: Creo, Intellego, Muto, Perdo, & Rego (actions Create, Perceive, Change, Destroy, & Control, all Latin verbs conjugated in the first-person singular); the Forms are: Animal, Auram, Aquam, Corpus, Herbam, Ignem, Imaginem, Mentem, Terram, & Vim (objects Animal, Air, Water, Bodies (human), Plants, Fire, Images/Sensations, Minds (human), Earth, & raw arcane Power, once again, all Latin, declined in the accusative case). Thus, Creo Ignem spells create fire (and the normal effects of fire, such as heat & light), while Perdo Imaginem spells destroy images and other sensory experiences (e.g. invisibility, inaudibility, making food & drink taste bland, etc.), and Creo Mentem spells can create ideas, memories, and intentions within a person's mind.

Magi have spells they study & learn (called "Formulaic" magic), but can also create new effects on the spur of the moment (called "Spontaneous" magic). Spontaneous magic is less powerful, but much more versatile, than is Formulaic magic. Magic is treated in this game-system as a serious object of study: magi are supposed to spend a long time in their laboratories, preparing new spells and potions, and increasing their knowledge of the Arts. The other main innovation was the insistence on play-acting the characters - indeed, many characteristics of the later Storyteller system developed by White Wolf Game Studio can be traced to Ars Magica (and the fact that both Ars Magica and the Storyteller system were both developed by the same person); White Wolf's Mage: The Ascension was envisioned as "Ars Magica in the Modern World," and many of the changes in Ars Magica's 3rd edition were introduced in order to make the game-worlds more compatible.

Ars Magica is an example of a Troupe System, although a number of campaigns (known as Sagas) will have most stories run by the same person, known as the Alpha Story Guide. For the length of a story (adventure) there will typically be more Companions than Magi. At the end of a story the players have the option of changing characters (becoming Magi, or Companion) or taking on the role of Storyteller.

Ars Magica was first published by Lion Rampant games, who also published the 2nd edition of the game. In the early 1990s, rights to Ars Magica were acquired by White Wolf, the company that Rein-Hagen had in the meantime founded. White Wolf published the 3rd edition, which greatly expanded the settings and peripheral rules while leaving the core system intact. White Wolf also published many supplements, detailing specific regions of Europe, or outlining stories that could be played in the original setting. Ars Magica was later sold to Wizards of the Coast, who produced several supplements, but just before publishing a 4th edition sold the rights to Atlas Games. Atlas published the fourth edition and has published new source-books since. The 5th edition has now been released by Atlas Games.