Jumping in Doom can describe two different mechanics: jumping by adding an upwards impulse to the player avatar via user input, which is possible in a number of popular source ports such as PrBoom+, DSDA-Doom, ZDoom, or GZDoom, where this mechanic can be bound to a specific key, allowing the player to jump in a similar way as is seen in other platform games, such as Super Mario Bros. or Prince of Persia; and jumping as is possible under vanilla Doom restrictions, more frequently referred to as platforming, where instead the player relies on horizontal momentum generated by running to allow them to run or fall over a gap between two platforms, thereby "jumping" from one to the other. The jump distance of platforming can be enhanced through straferunning, which increases the maximum speed and momentum of the player, as well as rocket jumping, which utilizes the horizontal backwards thrust generated by an exploding rocket, and arch-vile jumping, where the combination of horizontal and vertical thrust applied to the player avatar by an arch-vile's attack is used to propel them across gaps and upwards onto otherwise unreachable ledges.
While jumping was not implemented in the original Doom engine, with neither Doom, Doom II, nor Heretic offering it, vertical thrust was already an included feature, with the arch-vile's attack showcasing the mechanic (or tornado attack of the iron lich in Heretic). User-controlled jumping was then added in both Hexen and Strife, which ran on an enhanced version of the Doom engine.
Without jumping, the maximum elevation that the player can step up is 24 map units of height (16 in Strife), allowing for the creation of "ridiculously low walls" that must be lowered or otherwise worked around before the player can reach what lies in plain sight behind, for example a power-up, key, or switch. However, the player avatar, in contrast to most non-flying monsters, is able to step up even narrow stairs. This has been used in designing pseudo-ladders to implement a climbing-like behavior for games which do not support special climbable walls. Running up stairs allows the player avatar to continue its movement in a ballistic curve beyond the top of the stairway, within a certain range (though this effect is rather limited). Furthermore, the vertical thrust of the arch-vile's attack can propel the player up to 55 map units in height, which combined with the aforementioned step height of 24 map units increases the maximum height the player can clear to 79 map units, though this can be further increased by stacking multiple arch-vile attacks onto each other. In source ports where looking up and down is allowed by the engine, firing an rocket at the ground beneath the player causes them to be lifted up by the knockback from the explosion to allow for vertical rocket jumping as seen in games like Quake or Half-Life. Some fan-made deathmatch maps are designed with areas only accessible via this type of rocket jumping. This is not possible in the original engine, however; firing an rocket at the player's feet in Heretic (with the phoenix rod) or Strife (with the mini-missile launcher) will only cause horizontal recoil.
When using a source port that allows for actual jumping in Doom or Heretic, it is often considered a cheat to use it, as it has the potential to break the intended progression of a map if the level was not designed with jumping in mind. Because of this, some source ports allow disabling jumping on a per-map basis with a keyword in MAPINFO. By contrast, platforming under vanilla restrictions has been used in speedrunning since the very beginning, with optimal routes through levels often taking full advantage of platforming techniques to skip sections of the map, which is not considered a cheat, as it only utilizes mechanics that were implemented in the original Doom engine.
Several popular mods feature jumping as a key gameplay mechanic for exploring the levels, such as Knee-Deep in ZDoom or Tribute. Others go even further and focus their entire gameplay on jumping and platforming, as seen in projects such as Jumpmaze or Jumpwad. Doom 64 EX allows access to a jumping feature not found in the original Doom 64 after completing the secret level (Hectic) using the three-key exit, via the "Features" menu where other cheats are found.