Full list of all 85 XCOM: Enemy Unknown achievements. It takes around 200 hours to unlock all of the achievements in the base game on Windows.
The base game contains 50 achievements, and there are 2 DLC packs containing 35 achievements.
Clear a UFO crash site with one soldier on Classic or Impossible difficulty.
Shoot down 40 UFOs.
Mind Control an Ethereal. Single player only.
Earn the "Excellent" rating in every performance category on a terror mission.
Staff the Research Labs with 80 scientists.
In a single game, shoot down one of each alien craft.
In a single game, complete every Foundry project.
Staff the Engineering Department with 80 engineers.
Kill an alien while flying. Single player only.
Build a Laboratory.
Complete a Very Hard abduction mission in five turns or less on Classic or Impossible difficulty.
Win a mission with an all-female squad. Single player only.
Beat the game on any difficulty.
Beat the game on Classic difficulty.
Make contact with the Ethereal hive mind.
Kill 50 aliens with explosive weapons.
Build the Gollop Chamber.
Gain access to the lowest level in your base.
Build a S.H.I.V.
Acquire 1000 credits in one month.
In a single game, complete every Autopsy.
Find a soldier with the Gift.
Successfully assault an Overseer UFO.
Kill 500 aliens.
Build the Hyperwave Relay.
Get satellite coverage over every country on one continent.
Build a suit of powered armor.
Build a Firestorm.
Advance one of your soldiers to Colonel rank.
Recover the Hyperwave Beacon.
Uncover the alien base's location.
Stun an Outsider.
Kill 150 aliens.
Build a Workshop.
Fulfill a Council request.
Capture a live alien.
Build a base facility.
Complete a mission without losing a soldier.
Shoot down a UFO.
Launch a Satellite.
Build an item.
Complete a Research Project.
Complete the tutorial mission.
Beat the game in Ironman mode on Classic or Impossible Difficulty.
Win a multiplayer match.
Beat the game on Impossible difficulty.
Have a soldier survive every mission in a full game.
In a single game, complete every Research Project.
Play a multiplayer match against someone with this achievement.
Win the game from each of the 5 starting locations.
Complete Friends in Low Places.
Complete Confounding Light.
Complete Gangplank.
Take your new ally into the final challenge.
Complete Confounding Light with more than 3 turns left on the timer.
Get a Soldier to have 5 modifications in single player
Field a squad where all members have at least two modifications (min. 4) and win the mission
Field a fully enhanced squad and win the mission
Kill a Muton Berserker in melee combat in single player
Use Collateral Damage to blow up a car in single player
Deploy three tactical subsystems on a single soldier in single player
Complete Furies
Deal with the newest global threat
Complete Deluge
Make certain of the new threat's location
Eliminate all alien waves
Get at least 4 kills with XCOM Base Security personnel
Kill an elite enemy Medic with explosive damage in single player
Cause an enemy to suicide
Augment a soldier in single player
Kill an elite enemy Sniper with one of your own snipers in single player
Jump two stories in one move in single player
Proc Combat Rush on the entire squad (min. 4)
Eliminate an enemy's shield and kill it on the same turn in single player
Beat a new special mission without losing any assets
Have your special-duty soldier kill three enemies in the same mission
Modify a soldier in single player
Eradicate the infestation
Stop a squad member from suffocating in single player
Beat the game without buying a Squad Size upgrade (Classic+ difficulty)
Field a squad with 4 augmented soldiers, each with a different base ability and win the mission
Field a squad consisting entirely of augmented soldiers and SHIVs (min. 4) and win the mission
Kill an enemy as it is psionically attacking you in single player
Kill an unseen enemy detected by a specially modified soldier in single player
Designate a highly decorated soldier as the Volunteer