The Standard format uses only the newest sets the game has to offer. The current block, the block that was released the previous October, and the most recent core set are all legal to play in a Standard deck. As you can tell from the name, Standard is the most commonly played format. Standard events are available year round at retailers and tournament venues worldwide, offering new players a great opportunity to enjoy a tournament setting with the cards they've recently purchased.
Current Valid Card Sets
Block and Set Rulings
Standard is made up of the two most recent blocks and the core set(s) that directly follow them. Cards rotate out of Standard in late September / early October when a new block is released.