Magic Systems
Hermetic Magic
Most of Ars Magica is written by the perspective of the Order of Hermes and details its own system of Hermetic Magic.
However, many other magical systems exist in Mythic Europe and are often encoutered and mentioned by various supplements.
Also, Magic is just one of the four known Realms of Power. Comparable effects may be obtained by the other three powers: Divine, Infernal and Faerie.
Previous Editions
In the Second Edition adventure The Tempest it is claimed that Hermetic Magic was developed by Bonisagus the Founder combining principles of the written systems of the Cult of Mercury with principles of Druidic Magic.