Da'wa is a classical Islamic concept which has been dramatically re-appropriated in modern times across the Muslim world. This dissertation explores the modern resurgence of da'wa – "inviting" to Islam, or Islamic missionary activity – through the lens of inter-religious relations, and within the two horizons Islamic history and modernity. It demonstrates, first, the close relationship that has existed between da'wa and inter-religious relations both in the past and in the modern period. Second, it sheds light on the diversity of da'wa in the midst of other religions by tracing two broad styles of da'wa throughout Islamic history: "bottom-up" and "top-down" da'wa. Finally, it argues that Muslim communities in colonial and post-colonial India shed light on these themes with particular clarity. Indian Muslims, this dissertation suggests, have made pioneering contributions to global da'wa, particularly with respect to their development of bottom-up styles of da'wa and what this dissertation calls "da'wa modernities." These arguments are developed in two parts. Part I provides an examination of da'wa in relation to other religions from the Qur'an to the modern period. Since few studies have examined Islamic history through these lenses, this represents a major contribution in its own right. Building on Part I, Part II analyzes two prominent Sunni da'wa organizations to emerge from the Indian subcontinent in the past century: the Tablīghī Jamā'at (TJ) and the Islamic Research Foundation of Dr. Zakir Naik (IRF). By investigating and juxtaposing the lineages, formative histories and inter-religious discourses of these movements and their founders, Part II elucidates both the unique contributions Indian Muslims have made to modern da'wa, and the diversity of Indian da'wa. In response to the political, social and inter-religious challenges they have faced in modern India, and through their fresh engagement with Islamic scripture and tradition, these movements have developed related, though distinct, bottom-­up styles of da'wa and da'wa modernities which have proven to be globally relevant. This dissertation thus makes a significant contribution to the study of da'wa in general and to the study of the Tablīghī Jamā'at. It also provides the first major scholarly study of Zakir Naik.