This volume commemorates the fortieth anniversary of the Five Power Defence Arrangements (FPDA), established in 1971 by Singapore, Malaysia, Britain, Australia, and New Zealand. It features contributions from regional and international scholars who analyze the primary motivations behind the alliance, its contributions to regional security over the past four decades, and its potential future roles amid emerging geopolitical trends and security challenges in the twenty-first century. The FPDA has been a significant confidence-building measure among its Southeast Asian members, enhancing interoperability and professional cooperation among their armed forces. Its inherent flexibility and adaptability have allowed it to effectively respond to changes in the geopolitical landscape and new security threats. As it enters its fortieth year, the FPDA continues to be a vital element of Asia's security architecture in an era marked by change and uncertainty.