An exploration of the neurological and behavioral mechanisms and processes involved in intrusive thinking. On any given day, unintended, recurrent thoughts intrude on our thinking and affect our behavior in ways that can be adaptive. Such thoughts, however, become intrusive and problematic when they are unwanted, become compulsive, or lead to socially or medically unacceptable behavior. This volume explores what goes on in our brains to create thought intrusions, and how these instrusions lead to maladaptive behavior.