The Theory at a Glance: A Guide for Health Promotion Practice (Second Edition) describes influential theories of health-related behaviors, processes of shaping behavior, and the effects of community and environmental factors on behavior. It complements existing resources that offer tools, techniques, and model programs for practice. Theory at a Glance makes health behavior theory accessible and provides tools to solve problems and assess the effectiveness of health promotion programs. For nearly a decade, public health and health care practitioners have consulted the original version of Theory at a Glance for guidance on using theories about human behavior to inform program planning, implementation, and evaluation. Theory at a Glance can be used as a stand-alone handbook, as part of in-house staff development programs, or in conjunction with theory texts and continuing education workshops. This guide provides a small number of current and applicable health behavior theories which are widely used for the purposes of cancer control, defining risk, and segmenting populations.