The past two decades have seen ample debate about processing instruction (PI) and its various components. In this article, we first describe what PI consists of and then address three questions: about the role of explicit information (EI) in PI, the difference between PI and teaching that incorporates production-based (PB) practice, and various factors that may moderate the impact of these treatments. Our review shows that while many studies find little difference between PI with and without EI and between PI and PB, the results vary depending on whether the comprehension practice (structured input; SI) is task-essential or not and whether the PB is communicative or not. Furthermore, PI tends to favor comprehension abilities and PB production abilities. This review also shows that almost all PI research so far has been very short-term and limited to a narrow range of structures and populations, typically American college students learning a foreign language. Therefore the implications that some have drawn from the PI literature, namely, that neither EI nor production practice help beyond SI, are still far from generalizable.