There are several different official sanctionable constructed formats in Magic. These formats are defined by which sets are legal to use when building decks. Because some cards appear in more than one set, it is legal to use a card from a previous set as long as the card was also printed in a current legal set.

For example, you can use a copy of Ghost Quarter from Dissension in a current standard deck. This is because Ghostly Quarter was also printed in Innistrad, a set that is currently legal in standard. In some cases, when a card is reprinted, its text will be changed, so it is important to be aware of the current official Oracle text of older cards.