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