In December 2012, just one day after assuming the premiership for the second time, Prime Minister Shinzo Abe published an opinion piece on the virtues of a Security (DSD). In the article, Abe called for the formation of a diamond to safeguard the maritime commons stretching from the Indian Ocean region to the western with four of Asia's most prominent maritime democracies--Australia, India, the United States and Japan--forming the points of the diamond. The Japanese leader explicitly called on these states to join forces to oppose Chinese coercion and to defend peace, stability and freedom of navigation within the diamond. The DSD idea represents the second time that Abe has attempted to form a security grouping among these four liberal democracies, the first being the failed 2007 Quadrilateral Initiative involving the same four countries. (1) The rehashed quadrilateral concept raises a number of interesting issues relevant to the future security environment of the Indo-Pacific, and for Southeast Asia in particular. With respect to the current security environment, regional architecture has been based on a network of United States-centric bilateral alliances and partnerships with countries such as Japan, Australia, South Korea, the Philippines, Thailand and Singapore. The burgeoning Japan-India relationship is a more recent bilateral development. Such bilateral relationships sit side-by-side with broader multilateral regimes such as the ASEAN Regional Forum (ARF) and the East Asia Summit (EAS). These and other multilateral regimes are important diplomatic forums, but they do not impose any security obligations on member states. In short, security relationships in Asia have been built on a number of bilateral networks. The DSD idea is significant because it potentially proposes a change or evolution of the existing security architecture based on bilateral relationships that has served Southeast Asian states well for many decades. With respect to Southeast Asia, all member states of the Association of Southeast Asian Nations (ASEAN) seek to ensure that the organization remains in the driver's seat--or maintains Centrality--when it comes to leading regional forums. Up to now, the security bilateral relationships in the region have not overtly challenged ASEAN's diplomatic standing or relevance. In contrast, and for some Southeast Asian states, a possible quadrilateral grouping such as the DSD--being built on the back of closer India--Japan ties--might be seen as a possible threat to ASEAN Centrality. Assessing individual and collective responses of Southeast Asian states to India-Japan developments and the DSD concept is an important part of the discussion. In addressing the above issues, this article has several aims. The first is to outline Abe's idea of the DSD, why Japan has recently advocated for its formation, and why the United States, India and Australia are targeted as potential members. The second is to discuss Japan's greater willingness and capacity to play a meaningful strategic role, applied to a DSD context. The third is to discuss deepening Japan-India strategic cooperation and assess the prospect of Indian support for the quadrilateral idea. The article assess what role India might play (taking account of India's force capabilities, existing regional relationships, maritime strategy and interests and its relationship with China), and its level of interest in joining such a grouping. Finally, the article suggests how key players in Southeast Asia might view closer security ties between Japan and India, and the prospect of a DSD being built on the foundation of this emerging bilateral relationship. The Democratic Security Diamond Prime Minister Abe's argument for the establishment of a DSD rests on a number of basic premises. The first is that the Pacific and Indian Oceans, and the seas in between them, represent a new centre of prosperity in the world, largely as a result of export oriented development and open markets for trade, made possible because of peace, stability and freedom of navigation in the region's oceans. …