Pacifist
Complete Deus Ex: Human Revolution without anyone dying by your hand. (Boss fights don't count.)
In concept, this trophy is simple: don't kill anyone. Starting at the very beginning of the game with the attack on Serif Industries, all the way through to the end of the game, do not take a life in any way, shape or form. What may be less obvious is that you cannot take a life indirectly either. Once you have incapacitated an enemy, make sure that they do not fall to their death from heights, drown in water, or die from some other environmental hazard. Also, you cannot program turrets or robots to attack enemies, as any deaths that are caused by a turret/robot under your control will count against you. Destroying a camera, turret or robot will not count as a kill however, so they can be eliminated without worry.
Obviously the four bosses that you fight are special cases, and do not disqualify you from the trophy.
NOTE: For the most part, after an enemy is incapacitated, you can tell if an enemy is living or dead by the icon that appears on the prompt when you aim at their body. It will show Zzz if the enemy is unconscious, or a skull if the enemy is dead.
This display is glitchy however, particularly among some of the Derelict Row Ballers, so another way of being sure is by the Merciful Soul bonus experience that you receive when you knock them out. I can personally verify that I experienced this glitch where it appeared as though an enemy was dead, and yet I still received the trophy once the game was completed. Experiences may vary, so be careful.