Book excerpt: In the Handbook of Understanding and Measuring Intelligence distinguished scholars Oliver Wilhelm and Randall W. Engle have assembled a group of respected experts from two fields of intelligence research--cognition and methods--to summarize, review, and evaluate research in their areas of expertise. Each chapter presents the state-of-the-art in a particular domain of intelligence research, illustrating and highlighting important methodological considerations, theoretical claims, and pervasive problems in the field.