Does instruction make a difference? This was the original question of a paper written by Michael Long (1983) in the 80s. Since then, scholars and practitioners have been debating on whether instruction makes a difference in the acquisition of language properties such as morphology and syntax. Contemporary theories have addressed this question by taking different positions around the role and effects of instruction. Researchers have investigated the effects of a number of different instructional treatments (e.g., textual enhancement, processing instruction, recasts). Overall, the main findings from empirical research on the effects of instruction seem to indicate that there are two main positions: (1) instruction has a limited and constrained role; and (2) instruction might have some beneficial effects (not on the route but on the rate of acquisition). Several key questions (VanPatten, Smith, & Benati, 2019) have been raised in this field about the nature and role of instruction and on what we really measure with instruction (explicit or implicit knowledge?).