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