The International Institute for Strategic Studies (IISS) is an international research institute and think tank focused on defence and security issues. Its headquarters have been at Arundel House in London since 1997, and it operates offices on four continents.

The institute produces data, research, publications and online analysis on defence, security and global affairs. It also convenes major international security summits.

In reporting on suspicious drone activity over NATO countries, the IISS has been cited for research examining patterns of drone flights over sensitive sites and their possible links to wider security threats.