The Block Constructed format uses only the cards from a single block of Magic sets. Magic sets since Mirage have come in groups (usually of three) known as blocks. Block Constructed formats, and blocks themselves, usually take the name of the first set in the block. For example, the Ravnica Block Constructed format consists of Ravnica: City of Guilds, Guildpact, and Dissension.Only cards that were printed in the sets in the appropriate block can be used in Block Constructed formats.
The Lorwyn block was the first block to contain only two sets, Lorwyn and Morningtide. However, this block is combined with the Shadowmoor block, which also only contained two sets, to make the Lorwyn-Shadowmoor Block Constructed format.