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