Book excerpt: Over the past thirty years, and particularly within the last ten years, researchers in the areas of social psychology, cognitive psychology, clinical psychology, and neuroscience have been examining fascinating questions regarding the nature of imagination and mental simulation – the imagination and generation of alternative realities. Some of these researchers have focused on the specific processes that occur in the brain when an individual is mentally simulating an action or forming a mental image, whereas others have focused on the consequences of mental simulation processes for affect, cognition, motivation, and behavior. This Handbook provides a novel and stimulating integration of work on imagination and mental simulation from a variety of perspectives. It is the first broad-based volume to integrate specific sub-areas such as mental imagery, imagination, thought flow, narrative transportation, fantasizing, and counterfactual thinking, which have, until now, been treated by researchers as disparate and orthogonal lines of inquiry. As such, the volume enlightens psychologists to the notion that a wide-range of mental simulation phenomena may actually share a commonality of underlying processes.