Complete the indicate task to unlock the corresponding costume.

Costume	How to Unlock:
Altair	Obtain the Assassin emblem
Business Suit	Complete the game.
Civilian Disguise	Start Eastern Europe level
Corpse Camo	Have at least 51 continues in a single playthrough.
Metal Gear Solid optical camo	Complete the game without going into alert phase. Alternately, purchase it from Drebin for 5 million Drebin Points after starting another game session after completing the game. This camo makes you completely invisible.
Middle East Militia Disguise	Middle East in the Militia Safe House
South American Rebel Disguise	South America (Cove Valley Village)