Flying

Flying is a gameplay mechanic officially added in Beta 1.8, the Adventure Update. It is the most versatile form of transportation and can only be used in Creative mode, although third-party mods can enable flying in Survival mode. Flying makes the Player move at around 10.8 meters/second (38.88 km/h), which is about 150% faster than the normal walking speed, being 4.3 meters/second. Flying decreases the Player's friction by a lot, making the player move as if they were on ice. If a player is flying in fluids they will not sink or slow down. Until the snapshot 12w17a the player would slow down when traveling in fluids, just like in survival.

Flying is not limited by any processes such as food depletion, which limits sprinting. Flying mode can be toggled by double-tapping the "jump" key and can be activated at any altitude. The player can gain or lose altitude while flying by pressing the "jump" or "sneak" keys, respectively. Since disabling flying mode initiates a small increase in altitude (due to the jump key also being the key for increasing altitude), if space above the Player is obstructed by a block (i.e. the Player runs into a block while gaining altitude), the Player will not be able to disable flying mode unless they lower the altitude or moves away until there are no blocks touching or close to touching the top of the player. Flying mode is automatically disabled if the Player lowers onto a surface while in the air. Flying increases the player's field of view by 10. A way to tell if you are flying or walking is to look at the Sun or Moon, which will zoom in or out during the mode change. Flying is useful in combat because the player can not only take its victim by surprise, but can also deal critical hits if moving downwards while attacking.

In Minecraft Pocket Edition, the player ascends or descends by sliding from the center button to the up or down button, respectively.

If the Player gets into a minecart or bed while flying, they will still be flying when they gets out of the minecart or bed.

Players flying in The Void will only receive Void damage if they are below altitude -64, allowing them to fly a short distance beneath bedrock.

Flying is usually not enabled on vanilla servers, so if the player is in Survival mode, and is in the air for an abnormally long time, they will be kicked.

History
Flying was added in Beta 1.8pre1, and was officially introduced in Beta 1.8. Players could fly before Beta 1.8pre1 but they had to use a mod which is still around today, it's known as Single Player Commands. To use it you have to have the mod installed and working and type /fly then you can fly.

Jeb tweeted about it, etc.

Bugs

 * When flying near unusual level surfaces such as Redstone Repeaters, it is possible to sink 1 block into the ground.
 * The Player can activate flying mode and fly up or down while sleeping, although the player cannot move the field of view.

Trivia

 * It is possible to sprint while flying, which gives a minimal speed boost. To do so, start sprinting and then activate flying.
 * If a player flies very close to, but not on the floor, he/she will make a large amount of stepping sounds when moving.
 * If your computer is laggy, it can be a problem to start or stop flying. This can usually be fixed by looking straight up, which will increase your fps in most cases.
 * If you switch from Creative mode to Survival mode ingame while flying by using mods (ex. Too Many Items), you will continue to fly, but the second you hit the ground you will be hurt or killed due to the accumulated fall damage
 * If you go high enough while flying in Creative mode, you will see the sun through the fog even if you look down. You can also see the clouds at this time.