The evolution of theories of etiology in epilepsy makes an interesting study at many levels: some theories reflect social and philosophical attitude; some, have proved totally erroneous and now even appear ridiculous; and others show scientific insight now lost and worth reappraisal. This chapter outlines the theories of etiology for the 100 years since the time of John Hughlings Jackson, whose writing has often been said to announce the dawn of modern epileptology. The focus on theories of causation of epilepsy was not on organic brain diseases, but on predisposing and exciting factors, on Jackson's emphasis on mechanisms, and on theories of inheritance, degeneration, reflex epilepsy, and auto-intoxication. The chapter talks about the works of J. Russell Reynolds, William Gowers, Cesare Lombroso, William Aldren Turner, and ends with a discussion on William Lennox, and the then current theories of etiology. Lennox reconciled his eugenic sympathies with his clinical work.