Psychiatrists, psychologists, neurologists, linguists and speech pathologists currently have no coherent theory to explain why we curse and why we choose the words we do when we curse. The Neuro-Psycho-Social Theory of Speech draws together information about cursing from different disciplines and unites them to explain and describe the psychological, neurological, cultural and linguistic factors that underlie this startling phenomenon. Why We Curse is divided into five parts. Part 1 introduces the dimensions and scope of cursing and outlines the NPS Theory, while Part 2 covers neurological variables and offers evidence for right brain dominance during emotional speech events. Part 3 then focuses on psychological development including language acquisition, personality development, cognition and so forth, while Part 4 covers the wide variety of social and cultural forces that define curse words and restrict their usage. Finally, Part 5 concludes by examining the social and legal implications of cursing, treating misconceptions about cursing, and setting the agenda for future research. The work draws on new research by Dr. Jay and others and continues the research reported in his groundbreaking 1992 volume Cursing in America. A psycholinguistic study of dirty language in the courts, in the movies, in the schoolyards and on the streets.