Since the mid-1960s, the Asian Development Bank (ADB) and the Association of Southeast Asian Nations (ASEAN) have both actively supported integrated regional developments. Regional cooperation and integration (RCI) lies at the heart of ADB's work because it is a powerful engine for economic growth and poverty reduction. In 2006, ADB adopted an RCI strategy comprised of four key pillars: cross-border infrastructure development; trade and investment; monetary and financial cooperation; and regional public goods. The chapter presents a description of the evolution of connectivity in the Greater Mekong Subregion, the multiple dimensions of connectivity under Master Plan on ASEAN Connectivity (MPAC), and the connectivity-competitiveness tie-in. ADB's support for MPAC began with its formulation and has continued into implementation. The chapter presents a summary of ADB's assistance to MPAC implementation through transport projects, transport and trade facilitation initiatives, energy projects, and the mobilization of financing via the ASEAN Infrastructure Fund.