This chapter concentrates on prominent ideologies, religious freedom, Protestant mission, and religious conversion in the context of Turkey. The republican-era ideologies are Kemalism and Islamism, undergirded by the late-empire ideology of Ottomanism. These compose the ideological soil that anchors the roots of this investigation. The Kemalist Turkish-secular synthesis and the Islamist Turkish-Islamic synthesis emerge as crucial conceptual constructs, foundational for understanding the emergence of a third conceptual construct (see Chap. 6). Empowered by an unprecedented version of constitutional religious freedom that was aligned with the Universal Declaration of Human Rights, Protestant mission in Turkey reached new heights of success, with conversion from Islam to Christianity and the establishment of ecclesial Protestant communities seemingly being integral contributing factors to the success. However, the existing literature provides no overarching narrative of the Turkish Protestant movement and no tenable explanation of how the factors of religious freedom, missionaries, converts, and convert communities have co-contributed to the movement’s emergence and expansion. In providing such a narrative and explanation, this study enriches the literature.