Haste

Haste is a keyword ability that allows a creature to circumvent summoning sickness. Creatures with haste can attack or use activated abilities with the undefined or symbol in the activation cost even if they have not been continuously controlled by a player since the beginning of that player's most recent turn.

Description
Haste has been in Magic since the original Alpha's Nether Shadow, though it did not have a keyword at the time and was simply spelled out in the rules text. In R&D, it was known by the nickname Celerity. Players used to refer to it as  Raging. It wasn't until the Sixth Edition rules change that it got added as a keyword ability. Haste has been rotated around the Color Wheel, initially being in black and green; it has now been placed primary in red, before black and green. Lately, green has moved up to secondary place, moving Black to tertiary. Green getting haste was a nod to constructed as a way to recover after board wipes.

For Future Sight, R&D explored the idea of putting haste on blue creatures (usually with 0 power) where the haste was about using the activated ability right away rather than attacking. This isn't something they have explored since.

Rulings

 * Haste removes the normal "cannot attack" restriction due to not being controlled at the start of a player's turn. It does not remove any other combat restrictions. For example, it will not make a Wall able to attack, give you a second attack in a turn, or allow you to attack using a Raging Goblin if the defending player has Island Sanctuary activated.

Enchantments that grant just haste
Target creature
 * Mark of Fury
 * Need for Speed
 * Instill Energy (attack only)

All your creatures
 * Emblem of the Warmind
 * Fervor
 * Fires of Yavimaya</c>
 * Temur Ascendancy</c>
 * Hammer of Purphoros</c>

All creatures
 * Concordant Crossroads</c>
 * Mass Hysteria</c>
 * Ashling's Prerogative</c> (match converted mana cost of the chosen value)

Planes card that grant Haste

 * Bloodhill Bastion</c> (whenever a creature enters the battlefield, also gains double strike)
 * Sokenzan</c> (all creatures)