This chapter discusses the emergence and development of the relationship between Southeast Asia and the Ottoman Empire and modern Turkey, concentrating on the three principal themes that defined this relationship: Islam, trade relations and politics. While particular attention is given to the Ottoman relationship with Aceh, their involvement with other Muslim polities on the Malay peninsula and archipelagic Southeast Asia is also considered. An overview is given of the state of the art of historiography in the field, as well as its broader relevance to the study of the Indian Ocean world and to the history of colonialism. The chapter also reflects on the Southeast Asian idealisation of Rum, as the Ottoman lands were known.