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