This article discusses international cooperation in merger control enforcement under competition law. It describes the framework of merger control in Japan, recent developments in international agreements, merger cases involving international cooperation, and the relevant governing authorities’ standard process, including waiver considerations. This article offers three contributions. First, it comments on international cooperation in merger control, including the necessity of confidentiality waivers. Second, it provides basic information for assessing the appropriateness and transparency of merger control policies. Finally, it encourages cooperation between young and advanced competition authorities. The article’s deep understanding of merger activity is based on a detailed analysis of the Japan Fair Trade Commission’s guidelines for international cooperation in merger control.