For Mandinga in Guinea-Bissau and Portugal, life-course rituals are currently provoking transnational debates on ethnic and religious identity. In Guinea-Bissau, these two identities are thought to be one and the same—to be Mandinga is to 'naturally' be Muslim. For Mandinga immigrants in Portugal, however, the experience of transnationalism and the allure of 'global Islam' have thrust this long-held notion into debate. In this article, I explore the contours and consequences of this debate by focusing on the 'writing-on-the-hand' ritual, which initiates Mandinga children into Qur'anic study. Whereas some Mandinga immigrants in Portugal view the writing-on-the-hand ritual as essential for conferring both Muslim identity and 'Mandinga-ness', others feel that this Mandinga 'custom' should be abandoned for a more orthodox version of Islam. Case studies reveal an internal debate about Mandinga ethnicity, Islam and ritual, one that transcends the common 'traditionalist'/'modernist' distinction. I suggest that the internal debate, although intensified by migration, is not itself a consequence of 'modernity' but has long been central to how Mandinga imagine themselves as both members of a distinct ethnic group and as practitioners of the world religion of Islam.