This book falls in the broad subject area of psycholinguistics and second-language acquisition. More specifically, this book is written for researchers stepping into the field of morphological processing so that they are not overwhelmed by the large number of individual studies and do not lose sight of the whole picture. With a comprehensive review of the relevant factors that first- and second-language morphological processing researchers need to take into consideration, including material- and procedure-related factors, participant individual differences, and participant group-level differences, this book is a useful theoretical reference work for morphological processing researchers. By considering the various potential confounding factors reviewed in this book, researchers are in a better position to more scientifically and meticulously reduce or eliminate the effects of potential covariates so that they can focus on their independent variables of interest. It may also help researchers in evaluating previous studies and their findings and whether or not these studies may have failed to consider possible confounding factors.