This handbook provides comprehensive coverage of assessment instruments used in mindfulness research. It discusses traditional and modern approaches used to develop psychometric measures and to establish their reliability and validity, such as classical test theory, item response theory and Rasch model, generalizability theory, facet benchmarking, and network analysis. The handbook provides information on conceptual foundations, development, and psychometric properties of assessment instruments used to measure mindfulness in children, adolescents, and adults. In addition, it provides similar information on scales used in specific contexts and for various purposes. It reviews behavioral, cognitive, and psychophysiological assessment measures of mindfulness. The handbook examines a broad range of psychological, physical health, and mental health, and related measures that are used in mindfulness research. This reference work enables researchers to choose appropriate measurement tools fora broad range of mindfulness research.