This book analyses prime ministerial leadership in Britain and Japan since 1980. Exploring the interplay between personal skill, institutional resources and situational context in explaining the varying power and agency of different British and Japanese leaders, it asks whether the skills, strategies and circumstances needed for effective leadership are converging across liberal democracies. Comparing Britain and Japan reveals leadership trends that might otherwise go unobserved. The book addresses questions important to aspiring politicians as well as scholars, including: What accounts for the short tenure of most Japanese prime ministers? Does comparison with Japan explain the rapid turnover in British prime ministers since 2016? How is the influence of party factions on prime ministerial power evolving in Japan? Are British political parties more factional than commonly acknowledged? And how do changes in media technology affect leadership opportunities and constraints? The book draws on the author's experience as a political researcher in both the British and Japanese parliaments and on interviews with over 40 politicians and political journalists working in both countries.