Identity has become an explicit focus of International Relations theory in the past two to three decades, with one case attracting and puzzling many early identity scholars: Japan. These constructivist scholars typically ascribed Japan a ‘pacifist’ or ‘antimilitarist’ identity – an identity which they believed was constructed through the adherence to ‘peaceful norms’ and ‘antimilitarist culture’. Due to the alleged resilience of such adherences, little change in Japan’s identity and its international relations was predicted. However, in recent years, Japan’s foreign and security policies have begun to change, in spite of these seemingly stable norms and culture. This book seeks to address these changes through a pioneering engagement with recent developments in identity theory. In particular, most chapters theorize identity as a product of processes of differentiation. Through detailed case analysis, they argue that Japan’s identity is produced and reproduced, but also transformed, through the drawing of boundaries between ‘self’ and ‘other’. In particular, they stress the role of emotions and identity entrepreneurs as catalysts for identity change. With the current balance between resilience and change, contributors emphasize that more drastic foreign and security policy transformations might loom just beyond the horizon. This book was originally published as a special issue of The Pacific Review.