Standard
Standard (formerly known as Type 2) is a rotating constructed format that allows for all cards in the newest two story-based blocks and the newest Core Set to be played, save for cards on the Standard Banned List.
Constructed decks must contain a minimum of sixty cards. There is no maximum deck size; however, you must be able to shuffle your deck with no assistance. If a player wishes to use a sideboard, it must contain exactly fifteen cards.
With the exception of basic land cards, a player's combined deck and sideboard may not contain more than four of any individual card, counted by its English card title equivalent.[1]
Current Rotation
These are the sets that are legal in the Standard format as of July 19, 2011 [1]:
Banned list
As of July 1st, 2011, Jace, the Mind Sculptor and Stoneforge Mystic will be banned in the Standard format [2]. The deck list for the "War of Attrition" Event Deck will be legal in Standard if kept completely intact. That deck, which went on sale on June 10, contains two copies of Stoneforge Mystic. [3]