IWAD

An IWAD - short for Internal WAD - is the main resource file for a Doom-engine game, containing all the game's original sounds, levels, and graphics. ZDoom needs an IWAD file in order to play; without one the ZDoom engine has no game data to use.

Supported IWADs

Notes:

Some file names are links to a page on the Doom Wiki where you will find checksums for known versions of the concerned file.
Some files have conflicting names; ZDoom provides you with possible aliases. Note that an IWAD is actually identified by its content rather than its name. Also, any archive format supported by ZDoom can technically be an IWAD.

Commercial games

Name	File name	File aliases	Notes and download links
Doom (Registered)	`doom.wad`		Buy on GOG.com — Buy on Steam
The Ultimate Doom	`doom.wad`	`doomu.wad`	Buy on GOG.com — Buy on Steam
Doom "BFG Edition"	`doom.wad`	`bfgdoom.wad`, `doombfg.wad`	Buy on GOG.com — Buy on Steam — Part of Doom 3: BFG Edition
Doom II	`doom2.wad`		Buy on GOG.com — Buy on Steam
Doom II "BFG Edition"	`doom2.wad`	`bfgdoom2.wad`, `doom2bfg.wad`	Buy on GOG.com — Buy on Steam — Part of Doom 3: BFG Edition; also loads `nerve.wad`
Final Doom — TNT: Evilution	`tnt.wad`		Buy on GOG.com — Buy on Steam
Final Doom — The Plutonia Experiment	`plutonia.wad`		Buy on GOG.com — Buy on Steam
French Doom II	`doom2f.wad`		No longer sold; a patch is available at Doomworld/idgames for the original English version.
Heretic (Registered or Commercial)	`heretic.wad`	`hereticsr.wad`	Buy on GOG.com — buy on Steam
Hexen (Full)	`hexen.wad`		Buy on GOG.com — Buy on Steam
Hexen: Deathkings of the Dark Citadel	`hexdd.wad`		Buy on GOG.com — Buy on Steam
Strife (Full)	`strife1.wad`	`strife.wad`	Buy on GOG.com — Buy on Steam — Also loads `voices.wad`
Strife: Veteran Edition	`sve.wad`		Buy on GOG.com — Buy on Steam — Also loads `voices.wad`
Chex Quest	`chex.wad`		No longer sold, originally distributed in cereal boxes.

Free-to-play games

Name	File name	File aliases	Notes and download links
Doom (Shareware)	`doom1.wad`		Doom shareware at Doomworld/idgames
Heretic (Shareware)	`heretic1.wad`		Heretic shareware at Doomworld/idgames
Hexen (Demo)	`hexen.wad`	`hexdemo.wad`, `hexendemo.wad`	Hexen demo at Doomworld/idgames
Strife (Teaser)	`strife0.wad`		Strife teaser at Doomworld/idgames
Freedoom: Phase 1	`freedoom1.wad`	`freedoomu.wad`	Official site
Freedoom: Phase 2	`freedoom2.wad`	`freedoom.wad`
FreeDM	`freedm.wad`
Blasphemer	`heretic.wad`	`blasphem.wad`, `blasphemer.wad`	Official site
Chex Quest 3	`chex3.wad`		Official site
Action Doom 2: Urban Brawl	`action2.wad`		Official site
Harmony v1.1	`harm1.wad`		Official site
Hacx v1.2	`hacx.wad`		Official site
Hacx v2.0	`hacx.wad`	`hacx2.wad`	WIP download thread
The Adventures of Square	`square1.pk3`		Official site
Delaweare	`delaweare.wad`		Official site
Rise Of The Wool Ball	`rotwb.wad`		Download thread

ZDoom will detect any of those present in its search path and let you choose at startup which game to play (if it doesn't, see the FAQ). In addition to them, some "total conversion"-type mods, such as Wolfenstein 3D TC, can be played as their own IWAD; however since they are not detected as such by ZDoom, you need to use the -iwad command line parameter.

In order to play a custom level designed for any of the above games you have to have that particular game's full IWAD (loading PWAD with shareware, demo or teaser versions is disabled). If you do not have the necessary IWAD, or if you have an old, unpatched version of the IWAD in question, you will get an error message on startup. (But often old versions are accepted too.)

The IWAD file(s) should be placed in a directory where ZDoom will find them. This includes the same directory as the ZDoom executable, as well as those pointed to by the DOOMWADDIR environment variable. You may also configure other directories for ZDoom to search in the zdoom.ini file. On Linux, the directories $HOME/.zdoom and /usr/local/share are checked by default. Finally, if you have bought a supported game from GOG.com or Steam, ZDoom is able to find the IWADs directly in their installation folder and you do not need to move or copy them to ZDoom's folder.

Obtaining IWADs

As noted aboved, some IWADs can be downloaded freely; however most "full" games are not and must be bought from one of the following sources:

GOG.com: This store offers downloadable versions of Ultimate Doom, Doom II: Hell on Earth (bundled with Final Doom and the Master Levels for Doom II), Heretic, Hexen, Hexen: Deathkings of the Dark Citadel, and Strife. The Final Doom version offered is the later Anthology version, which fixes many mapping errors (such as the infamous missing key in TNT MAP31).
Steam: This store offers downloadable versions of Ultimate Doom, Doom II: Hell on Earth, Final Doom, Heretic: Shadow of the Serpent Riders, Hexen: Beyond Heretic, Hexen: Deathkings of the Dark Citadel, and Strife; as well as the Master Levels for Doom II which is a set of PWAD, not an IWAD.; Warning: following the release of Doom 3: BFG Edition, the Master Levels are no longer available to purchase individually but can be bought as part of the Doom Classic Complete Pack.; Note: The version of Hexen: Death Kings available on Steam is not patched. You need to download and apply the Death Kings 1.1 patch first. (The "readme.txt" file it tries to patch has been renamed readme-dk.txt by Steam, but is not important.) All other IWADs from Steam are fully patched.
Amazon.com, eBay.com, etc.: Second-hand copies of the original games can be found on such sites.
Flea markets, used-games bins in brick-and-mortar stores, etc.: It's mostly a matter of luck, but they can still sometimes be found this way.

Custom IWADs

Since version 3.2, GZDoom allows to define custom IWADs that can be detected without having to update the engine's own internal list. These custom IWADs need to have the .iwad or alternatively .ipk3 (not the traditional .wad and .pk3) extension, and they need to include an IWADINFO lump.