This open access book, updating a 1999 volume, is a resource for researchers who study religion and spirituality either as an interest in its own right (e.g., psychologists of religion) or in relation to some other variable such as physical or mental health (e.g., medical researchers). In the past few decades the study of religion in psychological terms has grown exponentially. Over this time, many measures have been developed, but are often difficult to find or have not been published at all. This volume offers a comprehensive listing and review of over 300 empirically valid measures that makes them easily accessible for scientific use. Belief systems are regarded as a critical factor in the health, both mentally and physically, of most individuals. This book provides a rich array of solidly researched means of assessing religiosity that can provide a scientific basis for psychological, sociological, and medical studies. It will serve researchers and clinicians alike in better assessing beliefs that are essential to an individual's health and behavior.