Mages Guild
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 Mercenary Guild once had considerable sway over the guild, and mages hoping to advance in rank would have to pledge fealty to Vychamp, its self-styled leader.
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.
 Maran Knights
Mara represents love and peace. She and Her Benevolence recognize that, as hypocritical as it sounds, military strength is often needed to beget this peace. The Maran Knights represent this military strength. They are a controversial knightly order. Some clerics within the Temple would prefer that the knights disband, but they are in the minority, and most citizens respect the knight's skill and loyalty.
 Mercenary Guild
The Mercenary Guild is a small guild led by Vychamp, its self-styled leader. The guild had considerable sway over the Mages Guild, and mages who wished to rise in rank needed to pledge fealty to Vychamp.
The Moot is a board of representatives, one from each Hold in Skyrim, which is convened upon the death of the High King of Skyrim to choose the successor from any qualified members of the royal family. In 1E 369, the Skyrim War of Succession began after the death of King Borgas. Imperial historians attribute the war to the Moot's failure to appoint "the obvious and capable" Jarl Hanse of Winterhold. The war, which lasted over 50 years and shrunk the Skyrim empire considerably, ended with the Pact of Chieftains, which dictated that the Moot only be convened when a King died without direct heirs. It has caused no similar problems yet. If there are direct heirs, the Moot still gathers to formally recognize the new High King, as they did for High King Torygg. The Moot can reconvene during a living High King's reign if he breaks some taboo which makes the Jarls of Skyrim lose confidence in him, such as refusing a challenge made in the old traditions.
 Morag Tong
The Morag Tong is an ancient guild of assassins headquartered in Morrowind, celebrating murder in the name of Mephala. They have been active since at least the First Era, and their targets have included multiple rulers of Tamriel, high-ranking Dunmer nobility, and countless others. The Morag Tong is unique in its sanctioned status under the Morrowind government to perform legal executions, bound under contracts called 'writs', although extralegal 'gray writs' are rumored to exist.
 Mythic Dawn
The Mythic Dawn was a secret cult that worshipped the Prince of Destruction, Mehrunes Dagon which brought about the Oblivion Crisis and thus the end of the Third Era. It plotted the assassination of Emperor Uriel Septim VII and his heirs as part of an attempt to lead a Daedric invasion of Tamriel. The Mythic Dawn's leader was Mankar Camoran, whose son Raven and daughter Ruma were his key lieutenants; of which all three were slain in 3E 433 by the Champion of Cyrodiil. The Mythic Dawn had many sleeper agents posing as regular townsfolk scattered throughout Tamriel, as well as a shrine to Mehrunes Dagon hidden in a cavern near Lake Arrius that served as their base. After the remnants of the Mythic Dawn were killed, Mehrunes Dagon's artifact Mehrunes' Razor was broken into four pieces. These pieces were hidden by several families, but were purportedly reunited in Skyrim during the Stormcloak Rebellion. A museum dedicated to the Mythic Dawn opened in Dawnstar in 4E 201.