Jumping

Jumping is a mechanic that elevates the player $1 1/4$ block into the air. It also has other effects when combined with another forms of movement.

Activation
Jumping is done by pressing the key (which defaults to the space bar on PC) or the jump button on other devices (for example the 'A' button on Xbox). If auto-jump is on the player jumps whenever they brush up against the edge of a block.

Usage
Jumping normally lets the player climb up 1$1/4$ block. Players with Jump Boost I are able to jump 1$15/16$ block, and with Jump Boost II they are able to jump 2$1/2$ blocks. The effect also increases more with more levels of Jump Boost.
 * Jump height changes

Honey blocks make players jump $3/16$ of a block from them, meaning that they get an 85% jumping reduction.

Cobwebs and sweet berry bushes prevent players from jumping from them.
 * Cancellation

Sneaking and crawling, when activated by suffocation prevention $$, prevent players from jumping due to the reduced space. These two actions normally do not prevent players from jumping.

Jumping can be combined with sprinting to increase the player's movement speed. This also reduces the hunger bar faster.
 * Combinations

Other mobs
Certain mobs are able to jump:
 * Villagers (but they prefer not to jump)
 * Illagers and witches when celebrating a successful raid, but otherwise do not jump when pathfinding
 * Foxes, when attacking prey
 * Spiders and cave spiders, when attacking
 * Rabbits, as part of their normal movement
 * The Killer Bunny attacks similarly to Spiders.
 * Other mobs can jump only if the player is luring the mob, or if the mob is hostile. If the mob flies, or is stationary, or is a water mob (except guardians, elder guardians and turtles), it does not jump.
 * Fishes flop around; they do not jump.

Trivia

 * Jumping was one of the first transportation mechanics added.
 * The highest possible distance a player can jump without effects is over 9 blocks, using ice momentum under a 2 block ceiling.