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