In this article I review processing instruction (PI), first introduced in VanPatten and Cadierno (1993). I outline a model of input processing, then describe the nature of PI itself, and follow this with a description of research to date on PI. I also review research that offers counterevidence to the findings of my own and others’ research and argue that some of these studies can be considered not as contradictory, but as complementary, to the research on PI, whereas some of the other studies contain drawbacks in design and procedure that merit close scrutiny.