This chapter addresses the topic of immigrant incorporation with a specific focus on multiculturalism. It highlights that although multiculturalism has been a defining characteristic of many Western societies since, at least, the last third of the twentieth century, it has faced considerable opposition over the past couple of decades on account of terrorism committed in the name of Islam, perceptions of Muslim minority communities as resistant to integration and of Islam as incompatible with Western society. The chapter discusses the claimed failure of multiculturalism due to Islam and Muslims and the retreat from it observed in many Western societies. It argues that the perception of Islam as a central contributor to the failure of and retreat from multiculturalism in the West is misplaced and proposes that closer attention needs to be paid to the role of the post-colonial, anti-Western ideology of Islamism in undermining multiculturalism in the West. The chapter contends that a failure to distinguish Islam from Islamism, not only among Western governments, media, and publics but within Muslim communities as well, has significantly contributed to unfavourable views of Islam in the West, perceptions of Muslims as undesirable citizens, and claims that multiculturalism has left Western societies vulnerable to unwelcome social change and threats to national security.