Legacy decks may consist of cards from all Magic card sets, plus the following cards: Sewer of Estark, Windseeker Centaur, and Nalathni Dragon (Mana Crypt would be included were it not currently banned).
Cards from expansions and special sets (like From the Vault, Commander, Duel Decks, Conspiracy, etc.) are legal in Legacy on the date of release of the expansion or special set.
Legacy is a constructed format and therefore adheres to the following constructed rules:
– Minimum of Sixty cards
– No maximum deck size, as long you can shuffle your deck unassisted
– Up to fifteen cards in your sideboard, if used
With the exeption of basis lands (Plains, Island, Swamp, Mountain, and Forest), Your combined deck and sideboard may not contain more than four of any individual card, counted by its English card title equivalent.
Note: The five snow-covered lands form the Ice Age block are also basic lands. Snow-Covered lands are only permitted in formats that allow expansions from the Ice Age block.
The banned & restricted list can be found here.