Hats (or Headwear) are items equippable in the 'head' slot of the loadout screen. Hats exist for purely cosmetic purposes, with the exception of the five Polycount Pack hats, which provide bonuses when worn with their associated weapons. In total, there are 73 unlockable hats available. Valve introduced the first set of 9 hats with the Sniper vs. Spy update. Many of following major updates added additional sets, including hats designed by members of the community.

Hats can be unlocked at random through the item drop system, and through the use of crafting system. But due to their significantly lowered chance to drop randomly and the higher crafting cost, they tend to be highly sought after and subject to great popularity within the community. They can also be bought from the Mann Co. Store.

In attempt to make hats more widely available without sacrificing the rarity of existing ones, Valve has made some hats available to players as a reward for completing in-game achievements. Other hats have been added as a bonus for special offers and promotions on games, including Left 4 Dead 2, Sam & Max: The Devil's Playhouse, Alien Swarm and Worms Reloaded.

There are currently a total of of 91 hats, including the 14 misc. items and the 7 limited edition hats