The Mages Guild was a professional organization, once located throughout Tamriel, that was dedicated to the study and application of magicka and alchemy. Its charter from the Emperor specified that the guild must provide magic services to the public. Anyone could purchase potions, alchemical ingredients, magical items, and a selection of standard spells from the guild. However, training, goods, and services were cheaper for members, and the guild stewards were sometimes able to provide members with work. Furthermore, exclusive services such as spellmaking and enchanting, deemed potentially dangerous to the public at large, were only made available to higher-ranked guild members in good standing.
The Mages Guild was led by an Arch-Mage, and guided by the Council of Mages, made up of five archmagisters (including the Arch-Mage). The Arch-Mage and the Council of Mages were headquartered at the guild's Arcane University in the Imperial City. The Council decided important Guild policies, such as its policy on the use of Necromancy and also administered recruitment, sale of spells in each local guild hall, and the enforcement of Guild law. In addition, guild halls existed in most cities in Tamriel, each of which was run by a local guildmagister.
The Mages Guild was founded by Vanus Galerion in the early years of the Second Era as a way of centralizing magic and thus moving away from the many separate groups (like the Psijic Order of which Galerion was a member) that had dominated the study of magic until that time. The Guild Halls were overseen by an Archmagister. Below him were the Master of Incunabula and the Master at Arms. The Master of Incunabula had a counsel of two, the Master of Academia and the Master of the Scrye. The Master at Arms also had a counsel, the Master of Initiates and the Palatinus (the leader of the local chapter of the Order of the Lamp).
The rules of the Guild varied from location to location, some differences more drastic than others. At the end of the Third Era, Hannibal Traven made a major policy change when he banned Necromancy from the Mages Guild. However, this was not a new policy: Vanus Galerion, the first Arch Mage of the Mages Guild, was strongly against Necromancy and most likely banned it. Regardless of whether or not Traven was following Galerion's beliefs, they still caused much unrest within the Guild. During this time, Mannimarco, the King of Worms, returned to Tamriel and nearly brought about the destruction of the Guild until Traven's successor, the Champion of Cyrodiil, stopped him and became Arch-Mage.
After the Oblivion Crisis, the Mages Guild was dissolved due to magic's reputation of having started the Oblivion Crisis. The two splinter organizations were known as the Synod and the College of Whispers.