This book looks into the accentual history of the Japanese and the Ryukyuan languages. Applying the comparative method, the author has reconstructed the accentual history of the Japonic languages. The reconstruction is based on modern dialects of Japanese and Ryukyuan, and also on historical materials. The investigation of ‘natural accent changes’ has allowed the author to formalize rules for accent change. Using these rules, the developments of the accent systems of descendant dialects or languages are explained. The development of typologically different accent systems is also explored.