Gottlob Frege has exerted an enormous influence on the evolution of twentieth-century philosophy, yet the real significance of that influence is still very much a matter of debate. This book provides a completely new and systematic account of Frege's philosophy by focusing on its cornerstone: the theory of sense and reference. This study represents a major reassessment of a seminal figure in the history of philosophy, and will be of particular interest to philosophers concerned with language and epistemology.