Motivation to read is a central consideration for teachers and researchers because it is strongly associated with reading performance and is generally accepted as a positive state. The study of reading motivation is plagued by inconsistent terminology and measurement, which impedes a comprehensive knowledge base for teachers and researchers. One of the most prevalent conceptualizations is intrinsic and extrinsic motivation to read. This review examines the research literature over the last 29 years on intrinsic and extrinsic reading motivation in an attempt to add clarity to the field regarding constructs and measurement. We identified study contexts, theoretical perspectives, and data sources to examine how literacy scholars have studied intrinsic and extrinsic motivation to read. Results provide an overview of the contexts, theories, and research designs used to investigate intrinsic and extrinsic reading motivation.