Southeast Asianists have a perennial tendency to question the reality of the region in which they are specialized. Yet while scholars have doubted, Southeast Asians at large have become increasingly sure that Southeast Asia does exist, and increasingly inclined to identify with it. This article summarizes a range of evidence to that effect, from opinion poll research and from the history of ASEAN and other pan-Southeast Asian institutions, and uses it to construct a critique of the relativistic view that Southeast Asia is a fluid and ill-defined concept. Southeast Asians today tend to see Southeast Asia as a cultural as well as a geographical and institutional unit. The nature of the perceived cultural unity remains unclear, and further research is called for in this area. There are reasons to think, however, that it reflects real inheritances from a shared past, as well as shared aspirations for the future.