Malayisation (Commonwealth spelling) or Malayization (North American and Oxford spelling) is a process of assimilation and acculturation, that involves acquisition (Masuk Melayu, literally "embracing Malayness") or imposition (Pemelayuan or Melayuisasi) of elements of Malay culture, in particular, Islam and the Malay language, as experienced by non-Malay populations of territories fully controlled or partially influenced by historical Malay sultanates and modern . It is often described as a process of civilisational expansion, drawing a wide range of indigenous peoples into the Muslim, Malay-speaking polities of Maritime Southeast Asia. Examples of Malayisation have occurred throughout Asia including in Brunei, Cambodia, Indonesia, Malaysia, Singapore, and Sri Lanka.
Malayisation started to occur during the territorial and commercial expansion of Melaka Sultanate in the 15th century, which spread the language, culture, and Islam to the Maritime Southeast Asia. Following the demise of Melaka in the early 16th century, instances of this assimilation of people from different ethnic origins into Malay culture, continued under numerous sultanates that emerged in Malay Peninsula, Sumatra, Riau Islands and Borneo. Malayisation could either be voluntary or forced and is most visible in the case of territories where the Malay language or culture were dominant or where their adoption could result in increased prestige or social status.
The ultimate manifestation of this cultural influence can be observed in the present dominant position of Malay language and its variants in Maritime Southeast Asia, the establishment of ethnic Malays realm within the region, the forming of new cultures such as the Peranakan, and the development of many Malay trade and creole languages.
In linguistics, the term Malayisation may refer to the adaptation of oral or written elements of any other language into a form that is more comprehensible to a speaker of Malay; or in general, of altering something so that it becomes Malay in form or character.