XCOM: Enemy Unknown and Enemy Within: Complete Guide

A strategy and tactics guide for Firaxis' 2012 XCOM: Enemy Unknown and its 2013 expansion Enemy Within, from your first Skyranger drop through the Temple Ship, including MECs, Gene Mods, Meld and EXALT.

Researched September 2026 — current as of the final PC release (no patches in years; the game is complete and stable). Live games change; check the linked sources if something differs.

What you own on Steam: XCOM: Enemy Unknown (app 200510) is the base game. Enemy Within is a paid expansion on PC (bundled with everything in the XCOM: Complete Pack). When both are installed, the launcher lets you choose which one to start. Enemy Within is the one to play: it contains everything from the base campaign plus a lot more. Everything below applies to both unless marked (EW).

Quick Start

• Play Enemy Within if you have it. It is strictly more content and better balanced. Start on Normal for a first run; Classic is the "real" difficulty the game is tuned around; Impossible is for veterans.
• Ironman is optional, not a badge. Ironman locks you to a single autosave. On a first playthrough, manual saves let you learn without a bugged mission ending your campaign.
• Never move into the unknown with your last action points. Advance with the first move (blue), keep the second (yellow dash) for reacting. Moving into fog with a dash is how pods activate on an exposed soldier.
• Full cover (shield icon filled) is everything. Half cover is barely better than nothing against aliens with height advantage or flanks.
• Overwatch is your default when you have no good shot. Aliens that move into view trigger reaction fire.
• Satellites win the strategic layer. Build Satellite Uplinks and Satellites early and keep launching them. Panic kills campaigns, and satellites are the main tool against it.
• Research the Arc Thrower and Xeno-Biology early. Live captures unlock interrogation credits and cheaper, faster research.
• Build the Officer Training School (OTS) as soon as it unlocks and buy Squad Size I and Squad Size II. Six soldiers instead of four is a huge difference.
• Rotate your roster. Wounds will bench your best soldiers; you need a B-team with some rank.
• (EW) Grab Meld canisters. They have a countdown timer, so push toward them with a plan. Meld pays for MECs and Gene Mods.

How a Campaign Works

The game alternates between two layers:

Layer | What you do | What matters

Geoscape (base) | Research, engineering, building facilities, launching satellites, intercepting UFOs, choosing missions | Money (credits, shown as the § symbol), Elerium, Alloys, Meld (EW), scientists, engineers, power, panic

Tactical | Turn-based squad combat, usually 4-6 soldiers | Cover, flanks, line of sight, action economy

Resources

• Credits come mostly from council funding at the end of each month. Each covered country pays more, and completing a continent's satellite coverage grants a continent bonus.
• Scientists speed research; you get them from mission rewards and satellite-covered countries.
• Engineers are required to unlock items and facilities; the Workshop adds them.
• Alloys and Elerium come from UFOs and alien corpses and weapon fragments.
• Meld (EW) comes from timed canisters on missions. Maps with Meld usually have two canisters: pick them up before their timers expire or they self-destruct.

Panic and the Council

Every country has a panic meter. Abduction missions give you a choice of three sites; the two you skip gain panic. Terror missions ignored cause a big panic spike. Countries at maximum panic at the end of the month leave the XCOM project, and if eight countries leave, you lose the campaign. Satellites over a country reduce panic when launched and give the scanning coverage that lets you catch UFOs.

Month-end rhythm

Satellites take time to build and launch. Launch them just before the Council report so the panic reduction and funding bonus land that month. Never let a month end with an empty Satellite Uplink slot and credits in the bank if a high-panic country is on the verge of leaving.

Tactical Combat Fundamentals

Concept | What it means | How to use it

Two actions per turn | Move + shoot, or dash (double move), or shoot then nothing | Shooting ends a soldier's turn for most classes

Full vs half cover | Full cover gives a big defense bonus, half cover a small one | Prefer full cover; half cover only when you have no choice

Flanking | An enemy with no cover between you and it | Flanked targets take bigger crit chance; do the same to aliens

Height advantage | Shooting from above gives an aim bonus | Rooftops and cliffs are premium real estate

Overwatch | Reaction shot on the next enemy that moves in view | Use when you can't get a decent shot

Hunker Down | Doubles cover bonus, removes flanking crit risk | For a soldier you can't move somewhere safe

Pods | Aliens patrol in groups that activate on sight and get a free "scamper" move | Reveal pods with one soldier, not your whole squad

The golden rules of movement

• Scout with one soldier. Move one soldier forward first, see what's revealed, then decide what everyone else does.
• Don't activate two pods at once. Fighting two groups at the same time is the most common way squads get wiped.
• Keep formation tight enough that everyone can shoot the same target but spread enough that one grenade can't hit three soldiers.
• Grenades beat bad aim. A frag grenade that guarantees destroyed cover or kills is better than a 45% shot.
• Explosives destroy corpses' loot value (weapon fragments), but a live soldier is worth more than fragments.

Soldier Classes

Class | Job | Signature abilities to know

Assault | Close-range flanker, shotgun specialist | Run & Gun, Lightning Reflexes (dodges the first reaction shot each turn), Close Combat Specialist, Rapid Fire, Killer Instinct

Heavy | Rockets, suppression, area damage | Fire Rocket, Bullet Swarm, HEAT Ammo (bonus damage vs robotic enemies), Shredder Rocket, Suppression, Danger Zone, Mayhem

Sniper | Long-range damage, overwatch | Headshot, Squadsight (shoot anything an ally can see), Snap Shot (move and shoot, with penalty), Double Tap, In the Zone

Support | Healing, smoke, utility | Smoke Grenade, Field Medic (extra Medikit charges), Sprinter, Revive, Savior, Deep Pockets

MEC Trooper (EW) | Armored augmented soldier | See the MEC section below

Promotion picks that matter

• Sniper: Squadsight vs Snap Shot is the defining choice. Squadsight lets the sniper sit far back and shoot targets revealed by teammates; Snap Shot lets them move and fire but with an aim penalty. Most players want at least one Squadsight sniper.
• Assault: Lightning Reflexes makes them excellent at triggering overwatch safely, which is a key utility against Thin Men and Mutons on overwatch.
• Heavy: HEAT Ammo is superb because Drones, Cyberdiscs, Sectopods and (EW) Mechtoids are robotic.
• Support: Field Medic early; Sprinter is a strong mobility pick for a Support that runs to downed allies.

Strategic Priorities (base and research)

Early research order that works

• Xeno-Biology then Arc Thrower (so you can stun and capture aliens)
• Alien Materials (Carapace Armor path) and Weapon Fragments into Experimental Warfare, which unlocks the Foundry
• Autopsies/interrogations as they come in; each interrogation gives a research credit that speeds related projects
• Laser Weapons, or lean toward plasma if you capture a live Muton early; interrogating a Muton cuts the research time of all Plasma weaponry
• Satellite production facilities running in parallel

Base building

• Power is the bottleneck. Put Thermo Generators on steam vents (they produce far more there). Excavating downward to find vents early pays off.
• Adjacency bonuses: facilities of the same type placed next to each other (Workshops together, Labs together, Uplinks together, Generators together) get bonuses. Plan a 2x2 block for Satellite Uplinks.
• Satellite Uplinks first, then a second as soon as money allows. Each uplink adds satellite capacity.
• Officer Training School early (Squad Size I and II, then Iron Will, Wet Work for faster XP).
• Foundry for key upgrades. Priority Foundry projects: S.C.O.P.E. Upgrade (+10% crit on the S.C.O.P.E.), Improved Medikit (needs Thin Man Autopsy), Ammo Conservation (needs Muton Autopsy; doubles shots per reload), Tactical Rigging (EW; two item slots for every soldier).
• (EW) Genetics Lab and Cybernetics Lab both unlock through Meld Recombination research.

Interceptors

Keep at least one Interceptor on each continent you have satellites over. Upgrade to better weapons (Phoenix Cannon, Laser Cannon, then Plasma Cannon or EMP Cannon) and consider Firestorm craft later. You can abort an interception you're losing without losing the craft.

Enemy Within: What It Adds

Meld

Meld canisters appear on most missions with a turn counter. Plan a route that collects both before their timers run out. Meld is spent on Gene Mods, MEC Trooper conversion, and MEC suits.

MEC Troopers

A soldier is converted at the Cybernetics Lab (costs credits and Meld, takes a few days). The conversion removes existing Gene Mods, and psionic-tested soldiers can't become MECs, so decide early who goes which path.

Suit tier | Name

MEC-1 | Warden

MEC-2 | Sentinel

MEC-3 | Paladin

Primary arm modules (pick one per tier):

Tier | Option A | Option B

1 | Kinetic Strike Module (huge melee punch, destroys cover) | Flamethrower (area damage, panics)

2 | Grenade Launcher | Restorative Mist (area healing)

3 | Proximity Mine Launcher | Electro Pulse (strong vs robots)

MEC abilities by rank: Collateral Damage (Squaddie); Advanced Fire Control or Automated Threat Assessment (Corporal); Vital-Point Targeting or Damage Control (Sergeant); Jet Boot Module or One For All (Lieutenant); Repair Servos or Expanded Storage (Captain); Overdrive (Major); Absorption Fields or Reactive Targeting Sensors (Colonel). One For All lets the MEC become full cover for allies; Absorption Fields makes a late MEC incredibly hard to kill.

Gene Mods

Built at the Genetics Lab after Meld Recombination. One mod per body slot:

Slot | Option A | Option B

Brain | Neural Damping (panic resistance, helps vs psi) | Neural Feedback (punishes psionic attackers)

Eyes | Hyper Reactive Pupils (+aim after a miss) | Depth Perception (bonus aim and crit from height)

Chest | Secondary Heart (bleed out instead of dying once) | Adrenal Neurosympathy (kill buffs nearby squad)

Skin | Bioelectric Skin (detect nearby enemies, strangle immunity) | Mimetic Skin (invisible when moving into full cover out of sight)

Legs | Muscle Fiber Density (jump to rooftops without ladders) | Adaptive Bone Marrow (faster wound recovery, heals in combat)

Good first picks: Depth Perception on Snipers, Adaptive Bone Marrow on anyone you rely on, Secondary Heart on your most valuable soldier, Mimetic Skin on a Squadsight Sniper (costly Meld-wise but extremely strong).

EXALT

EXALT is a human organization that runs cells in countries. Each month cells can sabotage you (steal credits, slow research, raise panic). Counter them:

• Intel Scan a region (costs credits) to reveal active cells.
• Launch Covert Ops: send one soldier undercover (very limited gear) and a squad later extracts them. Missions are Covert Extraction or Covert Data Recovery types.
• Each successful op reveals clues about EXALT HQ's country. When you're confident, accuse that country to launch the final assault. A wrong accusation has a penalty, so gather clues first.
• EXALT operatives can be stunned and captured with the Arc Thrower like aliens.

New aliens (EW)

• Seekers: cloaked flyers that sneak up and strangle an isolated soldier. Keep soldiers close together; Bioelectric Skin makes a soldier immune.
• Mechtoids: Sectoids in armored suits that attack twice. Sectoids nearby can mind-merge to shield them; kill the Sectoids first.

Special EW missions

• Operation Progeny: a three-mission chain (Portent, Deluge, Furies) that ends with a powerful psionic recruit.
• Site Recon: a Council mission to a Chryssalid-infested fishing village in Newfoundland. Only Chryssalids and Zombies; reach the ship's bridge to activate the transponder, then get out before the airstrike. No loot, since the area is bombed.
• XCOM Base Defense: aliens attack XCOM HQ roughly two to three weeks after you assault the Alien Base. Keep a decent B-team at base.

Alien Threat Cheat Sheet

Enemy | Threat | Counter

Sectoid | Mind Merge buffs another Sectoid | Kill the Sectoid that cast the merge; its partner goes down with it

Thin Man | Poison spit, leaps to high ground | Overwatch; stay spread out vs poison

Floater | Launches to flank | Keep full cover facing multiple angles

Muton | Grenades, Blood Call (buffs other Mutons), Intimidate (wounding one can panic the shooter) | Stay out of grenade clumps; use Arc Thrower for a capture

Chryssalid | Melee zombifies soldiers | Kill fast; overwatch traps; don't let it reach your line

Cyberdisc | Heavy damage, death explosion | HEAT rockets and grouped fire

Berserker | Charges on hit | Only shoot when you can kill it that turn

Heavy Floater | Grenade launcher from the air | Height and cover

Ethereal | Psi abilities, reflects fire | Mind Shield and focus fire

Sectopod | Huge damage, clusters | Separate your squad; focus all firepower

Common Mistakes to Avoid

• Dashing into the fog. The yellow move into unexplored ground has killed more soldiers than anything else.
• Skipping the Arc Thrower. Captures reward you with much cheaper research credits and are how you get specific research like Plasma weapons faster.
• Letting panic snowball. Choosing abductions only by reward is how you lose Nigeria or Egypt in month three.
• Building Labs you don't need. Scientists from satellites and missions usually outpace Labs; build Workshops and Uplinks first.
• Not saving a B-team. Wounds bench soldiers for weeks.
• Selling everything. Keep some alloys and Elerium for Foundry and interceptor upgrades; check the Grey Market wisely.
• Firing at a Berserker or Chryssalid you can't kill. Wounded ones get angrier.

Advanced Tips

• Overwatch trap setups. Set overwatch on 3-4 soldiers, then move one soldier to draw a pod into your line.
• Squadsight + Battle Scanner lets snipers shoot without anyone seeing the target first.
• Cash out the Council requests that fit your plan; they often give scientists, engineers or credits in exchange for items you already have.
• (EW) Covert operatives' best gear is limited, so give the job to a soldier who can afford to sit out; your best Sniper shouldn't go.
• Second Wave options change the rules. Damage Roulette, New Economy, Not Created Equally (random starting stats) and Hidden Potential are available from the start; more (such as Red Fog, Marathon, Results Driven, E-115) unlock as you win on Normal, Classic and Impossible. Try Not Created Equally on a second run.
• The Long War mod (for Enemy Within) dramatically expands the game: more classes, bigger squads, harder strategy. Only install it after a vanilla run; it is not beginner-friendly.

Missables and Completion Notes

• The Base Defense mission (EW) happens once; keep a capable B-team at home.
• All Progeny, Slingshot and Site Recon missions are one-time events in a campaign.
• Slingshot is a DLC mini-campaign of three missions (Friends in Low Places, Confounding Light, Gangplank); the first unlocks the soldier Zhang. It plays alongside the main story if enabled.
• Ending choice: the final Temple Ship mission requires a psionic volunteer, so start psionic testing once you can.

FAQ

Should I play Enemy Unknown or Enemy Within first? Enemy Within. It's the full base game plus new units, missions and systems, and it's the version the community treats as definitive.

What difficulty should I pick? Normal for a first run, Classic once you understand flanking and satellites. Classic Ironman is the classic "real" experience.

Why did my 95% shot miss? The game uses real percentages; 95% still misses 1 time in 20. Plan so a single miss doesn't lose the turn.

How many countries can leave before I lose? Eight. Keep satellites flowing and watch panic every month.

Should I rush Laser or Plasma weapons? Lasers are a reasonable bridge, but capturing a live Muton makes Plasma much cheaper. Many players go lasers for rifles/snipers and plasma afterward.

Is it worth playing XCOM 2 after this? Yes, but XCOM 2 is a separate game with different systems. This game's story finishes at the Temple Ship.

Does it run on modern Windows? Generally yes through Steam. If the 2K launcher gives trouble, launching the game directly from its Binaries folder is a common workaround.

Sources

• Wikipedia — XCOM: Enemy Within
• UFOpaedia — Strategy (EU2012)
• UFOpaedia — Gene Mods (EU2012)
• UFOpaedia — MEC Trooper (EU2012)
• UFOpaedia — Missions (EU2012)
• UFOpaedia — Second Wave (EU2012)
• UFOpaedia — Foundry (EU2012)
• Steam store — XCOM: Enemy Unknown