Health psychology is maturing to include both major studies relating IVs to DVs as well as in-depth investigation of how these relations occur and for whom. These analyses reflect the richness of data collected in investigations of health and hold the promise of uncovering important pathways by which psychological factors influence health. From a methodological standpoint, investigation of mediation and moderation represents how a third variable may be incorporated in statistical analyses to uncover underlying mechanisms, differing effects on unique populations, or conditions under which an effect may be pronounced or diminished. Often the addition of these measures to research projects costs very little, but offers tremendous potential to yield detailed information critical to the advancement of theory and practice in health psychology. (c) 2008 APA, all rights reserved