This paper reviews six issues that are key to understanding processing instruction (PI): (1) the distinction between processing and noticing; (2) the na ture of input processing; (3) the nature of language (i.e., what gets acquired); (4) the distinction between knowledge and skill; (5) the explicit/implicit "debate"; and (6) the distinction between method and intervention. The goal of the paper is to clarify misconceptions about the nature of PI and what it purports to effect, thus distinguishing it from other pedagogical interventions such as text enhance ment, recasts, and dictoglosses. In so doing, the paper offers six summary state ments that, together, form the foundations of PI.