Southeast Asia has long been known for its ethnic and cultural diversity. The ASEAN motto ‘Unity in diversity’ echoes this heritage, but refers to differences among, rather than within, the Southeast Asian nations. However, regional integration, labour migration and globalisation have given new salience to tensions between national culture and diversity and in so doing have highlighted once more the cultural richness and plurality within nation states. In spite of marked differences between ASEAN members, an analysis of national museums demonstrates significant parallels between their exhibitions. This talk focuses on the national museums and galleries of Thailand, Singapore, the Philippines, Malaysia and Indonesia, drawing on fieldwork carried out in 2017-2019. In these museums, pre-colonial heritage is often portrayed as the organic, uncontaminated bedrock of national cultures and histories. In some cases, the reinterpretation of World War II employs personal stories and plays on emotions to promote unity and nationalism. In these exhibitions, representing heroes, national icons and common people highlights the politics of defining the contours of the nation. Moreover, most of the museums studied frame the complexity of diversity and its politics through hierarchies of cultural markers. The talk will illustrate these patterns with images of the exhibitions as well as observations and recordings from the speaker’s fieldwork.