The paper explores the historical and ideological origins and theoretical underpinnings of Turkish nationalism in the late Ottoman period and the early republican era. The study draws on relevant sources and literature on the topic and builds on underlying theories of nationalism and identity studies. Under Ottoman rule, the multiethnic and multireligious populations of the empire were bound by their belonging to the common homeland, the Ottoman nation, and the ideology of Ottomanism, regardless of their ethnic origins. However, the decline of the Ottoman Empire and the rise of Greek, Armenian, Serbian, and other minority nationalisms led to the decline of Ottomanism as the hegemonic ideology. This process also induced the emergence of Turkish nationalism. The genesis and promotion of Turkish nationalism and Turkishness by Ottoman intellectuals at the end of the 19th century led to the erosion of Ottomanism. The transition from the Ottoman era into the republican period was marked by the nationalization of Turkish society. The nation-building project implemented by Mustafa Kemal and his followers aimed to transform Turkish society from a traditional and Islamic society into a secular, modern, progressive, and Western one. The results of the study have shown that the establishment of the Republic of Türkiye was not a mere transition from one period to another, but the inception of crafting a new nation premised on Turkishness. The Kemalists focus more on creating a unified national identity by Turkifying Muslim ethnic groups, while maintaining separate identities for Christian and other religious minorities. The results of the study have also indicated that Kemalist nationalism has pursued a policy of displacing and marginalizing the Ottoman past and Islam. Furthermore, the study shows that alongside the dominant Kemalist nationalist discourse, Turkish society also hosts other competing and overlapping nationalist ideologies and political groups. This is particularly evident in the emergence of non-Kemalist discourses and the rise of the AKP to power. The ascent of the AKP has indicated the persistence of alternative nationalist ideologies and discourses that were displaced and suppressed by the Kemalists, specifically Ottomanism, which has become a powerful discourse in both domestic and foreign policy in Türkiye.