Basic Engineer strategy

The Engineer has the unique ability to construct Buildings. Although he possesses a weaker set of weapons, his Sentry Gun is more than enough to fend off multiple enemies. His Teleporter system sends teammates to the front lines, while his Dispenser heals and supplies ammunition. After constructing a building, he can pick up and haul it to a new location, allowing him to keep his base alongside an offensive push. The Engineer and his buildings will frequently be targeted by Demomen and Spies. A well-timed enemy ÜberCharge, in particular, can quickly ruin all of his hard work. When his buildings are destroyed, it is most important that the Engineer makes it out alive so that he can reconstruct his base. A good Engineer will place his buildings in strategic locations and not be afraid to get his hands dirty defending them.

Primary Weapons

Shotgun

The Shotgun is a deceptively powerful weapon at close to medium range. Use it to defend yourself when alone and scare off enemies that your Sentry Gun cannot target. Choose the Shotgun over the Frontier Justice if you need to deal consistent damage over time.

Frontier Justice

Barring magazine size, the Frontier Justice is statistically identical to the Shotgun. You'll get the most of the Frontier Justice if you place your Sentry Gun in an offensive position, where it should be able to get a few kills or assists before being destroyed and granting you Revenge crits. Even if you have stored up a great number of Revenge crits, the small magazine size in addition to the threat of losing all of them upon death will prevent you from going on a mini-rampage. Equip the Pistol alongside the Frontier Justice so that you can conserve your Revenge crits. Although you can destroy your own Sentry Gun and still receive Revenge crits, the firepower of your Sentry Gun is generally more valuable.

Widowmaker

This weapon rewards accuracy. Accurate, close range shots will often give you more metal than it took to pull the shot off. Medium or long range shots, however, will often times expend more metal than it replaces. Critical hits will often times almost refill your metal as well. Use this weapon in close quarters where metal refills aren't present or you don't have a Dispenser up yet.

Secondary Weapons

Pistol / Lugermorph

You have a tremendous supply of Pistol bullets, so feel free to spam them at any enemies. Its effectiveness at medium range makes it combo well with Combat Mini-Sentry Guns.

Wrangler

Use the Wrangler to give your Sentry Gun extra staying power and allow it to attack enemies outside its normal range. Don't be afraid to allow your Sentry Gun to function normally; its AI is more aware and accurate than you are. By firing at yourself, you can Sentry jump to unusual locations.

Short Circuit

The Short Circuit is more useful for destroying enemy projectiles than attacking enemies. Use this weapon to quickly destroy projectiles such as rockets and grenades in mid-flight. It is also great for destroying sticky bomb carpets to protect your buildables and to allow safe passage for your teammates.

Melee Weapons

Wrench / Golden Wrench / Saxxy

Hitting buildings with your Wrench will cause them to build twice as fast. When using the Wrench, the game prioritizes repairing buildings over melee combat. Thus, if you attack an enemy Spy next to a friendly structure, you will hit the building instead of him. Use your Shotgun, which deals greater damage, to dispatch nearby foes instead.

Gunslinger

The additional health the Gunslinger grants makes you a viable attacking force; use your Shotgun and Pistol to complement Mini-Sentry fire. The offensive playstyle complements the Revenge crits you can receive for your Frontier Justice.

Southern Hospitality

The bleed effect the Southern Hospitality afflicts can be useful in a one-on-one fight and helps to track down Cloaked Spies. If a Pyro manages to corner you, you're probably going to die anyway, making the fire vulnerability negligible.

Jag

The Jag will let you build or redeploy buildings very quickly and is particularly useful for when you need a Sentry Gun at a forward location. It is a weak weapon, so use your Shotgun against close foes instead.

Buildings

Sentry Gun

It's best to place Sentry Guns in well-frequented areas to prevent enemies from passing entirely. When placing a Sentry Gun, note where it can shoot and where the enemy can fire from. If a Sentry Gun is placed out in the open, it can cover more ground but will be left more vulnerable to attackers. If placed in a corner, it is naturally protected from flanking by walls, but can only focus on a certain angle of the battlefield. The difference between excellent and average Sentry Gun placement can be very small. Moving it even a few inches can keep it from being picked off by Soldiers or Snipers. Avoid "gimmicky" Sentry positions such as looking down holes in ceilings, in the middle of narrow hallways, or around sharp corners; a Sentry Gun is useless if it can't fire at anyone.

Combat Mini-Sentry Gun

Due to their small size and quick build time, Mini-Sentry Guns can often be placed in positions that a normal Sentry Gun cannot and perform exceptionally well when laid in concealed areas. These advantages, coupled with the bonus health the Gunslinger provides, allow for relatively aggressive play. They only cost 100 metal to deploy, so you should be able to provide a constant source of suppressive gunfire. Don't hesitate to place them out in the open as distractions or to cover a retreat; players tend to fire at them before you. They are far less useful when placed in defensive positions, where their reduced firepower won't be able to fight enemies off.

Dispenser

A Dispenser is typically the first building you want to construct so that you have a stable source of metal. Placing Dispensers in forward locations will keep teammates healthy and allow them to hold an area for a long period of time. Additionally, because the Dispenser is a solid object, you can hop on your own Dispenser to climb to inaccessible places or block narrow passages from enemy Spies.

Teleporter

Always have a Teleporter system active to help a steady tide of reinforcements reach the front lines, even if the distance covered is short. Rotate the Exit so that it faces away from a wall and allows teammates to see the battlefield immediately upon coming through. Be aware that the Teleporter Exit's placement can impact the flow of battle; sending teammates to poor locations will weaken both your offense and defense. If either Teleporter member comes under fire, hitting one end with your melee weapon will repair the other. If guarding your buildings, refrain from standing on your Teleporter Exit, as enemy Spies are able to come through and telefrag you.