This open access book aims to review the history, achievements, and challenges of trilateral cooperation among China, Japan, and South Korea in a systematic way. It offers numerous perspectives to explain the emergence of trilateral institution-building processes and the fluctuations of trilateral cooperation, and underscores three countries’ respective policy stances towards the building of the triangle. The evolvement of political and economic ties among China, Japan, and South Korea has vital importance to the peace and prosperity of East Asia. Recent years have witnessed the ups and downs of the trilateral cooperation among the three countries. The development of trilateral institution building emerged as a joint gesture in response to the Asian Financial Crisis in the late 1990s. The three countries jointly established multilayered cooperative mechanisms in a wide range of fields. Nonetheless, trilateral cooperation among the three major powers has been proceeding in hardship in the shadow of longstanding geopolitical complexity and the deepening Sino-US confrontations. This book argues that, despite growing economic and social linkages, political animosities have constantly impeded the trilateral cooperation. Relevant to scholars and advanced students in international relations and political economy, this is a vital read in East Asian studies.