Range construction is the systematic process of defining which hands to play and how to play them in each position and preflop and postflop situation. A well-constructed range considers the balance between value hands and bluffs, table position, opponent tendencies, and stack sizes. Modern solvers have revealed that optimal ranges differ significantly from human intuition, including unexpected hands in some lines and excluding seemingly obvious hands in others. Mastering range construction is fundamental since a mistake in range building propagates to all subsequent streets.