At this point, Assassins Creed has a long and storied history, and that history (and the game's future, for that matter) are referenced numerous times in the form of tons of unlockable outfits and skins. Costumes are unlockable in both the single player and multiplayer; this guide will cover the single player requirements for unlocking every costume.

Kanien'keha:ka Outfit: During Mission 2: Feathers and Trees or Sequence 4: Heroes are Born, collect all three of the feathers to unlock this outfit.

Jamestown Outfit: Simply finish Sequence 6: Tea is for Englishmen, to unlock this outfit.

Charleston Outfit: Finish Sequence 6: Tea is for Englishmen.

Jamestown Outfit: Again, just finish Sequence 6.

Baltimore Outfit: Finish Sequence 7: The Whites of their Eyes.

New York Outfit: Finish Sequence 7.

Philadelphia Outfit: Finish Sequence 7.

Captain Kidd's Outfit: Finish the mission entitled "Location: Oak Island Naval to unlock this outfit.

Achilles' Outfit: Complete the mission "Achille's Painting to unlock this outfit.

Altair ibn La'Ahad's Outfit: Complete every single one of the "Optional Objectives" to unlock this outfit.