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