The Singapore Institute of International Affairs (SIIA) is a non-profit and independent think tank committed to producing policy analysis, fostering in-depth dialogues and bridging gaps between policymakers, private sector decision-makers and experts to shape public policy and social responses. Centred around ASEAN focused themes, the institute aims to deliver policy analysis in international affairs and on issues driving environmental sustainability. SIIA also plays a key role in Track II diplomacy, supplementing official dialogue between governments.

Established in 1962, the SIIA is a founding member of the ASEAN Institutes of Strategic and International Studies (ASEAN-ISIS), a regional alliance of think tanks. The Institute is a membership-based organisation, bringing professionals and thought leaders from all sectors to the fore for robust discussions that catalyse positive change in society.

Since 2012, the SIIA has been consistently ranked as one of the leading think tanks in Southeast Asia and the Pacific, in the Global Go-To Think Tank Index by the University of Pennsylvania. In 2017, the SIIA was ranked the No. 1 independent think tank in Asia. It was also recognised as one of the top 50 think tanks globally, excluding the United States of America.