I will discuss my research on psychological aspects of the porous divide between the physical and the mental, including the knowledge bases used to make these rudimentary determinations. A first series of studies explores chronic differences in the dominance of mental and physical experiences, the social and individual sources of physical or mental attributions, and cultural and health implications of these judgments. A second series concerns how overlap in the contents of mental intentions and physical behavior can yield false memories for behavior: The mistaken belief of having enacted a behavior when the behavior was merely intended. These false memories are more prevalent when decision encoding is difficult, when gist (vs. detailed) processing is involved, and when intention-behavior confusability is high. Implications for health interventions and medication adherence are discussed.