Processing Instruction (PI) research has been of interest to the readership of Studies in Second Language Acquisition since VanPatten and Cadierno published the original study on PI there in 1993. In a previous volume James Lee and Alessandro Benati identified five research branches: the effects of Processing Instruction compared to the effects of other types of instruction; the effects of full Processing Instruction compared to the effects of structured input activities and explicit information; the effects of structured input compared to the effects of aurally and visually enhanced structured input; the effects of Processing Instruction measured over time; and the effects of delivering Processing Instruction in classrooms to groups of learners compared to delivering it in computer laboratories to individuals. What is missing from the database is an extended examination of the role that individual differences might play in the results generated by Processing Instruction. This book gathers together research on Processing Instruction that addresses individual differences in the research design and/or analyses. This collection of essays will open an additional branch of PI research.