This is a comprehensive history of a concept that dominated philosophy and scientific methodology between the 1930s and the 1960s. The verificationist principle - the concept that a belief with no connection to experience is spurious - is the most sophisticated version of empiricism. More flexible ideas of verification are now being rehabilitated by a number of philosophers. The author surveys the precursors, the main proponents and the rehabilitators. Unlike traditional studies, she follows verificationist theory beyond the demise of positivism to examine its reappearance in the work of modern philosophers. Most interestingly, she argues that despite feminism's strenuous opposition to positivism, verificationist thought is at the heart of much of contemporary feminist philosophy.