There are 20 Space Marine Legions in Warhammer 40K, two of which are unknown. The canon is fluid, dating back to magazines and books released in the 80s, so it’s hard to verify exactly when each Legion was first mentioned, but thanks to dedicated fans we have a clue.

The Legions, once called Legiones Astartes, were created by the Emperor of Mankind to conquer the galaxy on multiple fronts. Each was led by a Primarch—the Emperor's genetically enhanced children with superhuman abilities far surpassing the Space Marines in their Legion—and each also had a different specialty.

There were 20 Legions, but at some point during the Great Crusade period of 40K lore, two of the Legions were completely erased from history and no one knows anything about them. When the Great Crusade ended and the Horus Heresy began, nine Legions joined Warmaster Horus to serve Chaos and were considered traitors. The Horus Heresy is probably the most famous event that 40K lore revolved around, and the Emperor ultimately triumphed over the wayward Primarchs and their Legions. Since then, the Legions have been divided into Loyalists and Traitors, depending on which side of the Horus Heresy each Legion joined.

Here are all the Space Marine Legions in Warhammer 40K, their Primarch and loyalties.