The Ismailis have a long, complex, and eventful history rooted in the Twelver Shi'a tradition of Islam, dating back to the 8th century CE. During the Middle Ages, the Ismailis split into two main groups, each following a different line of imams or spiritual leaders. The larger branch, the Nizari Ismailis, followed a line of imams, now represented in modern times by the Aga Khans, while the Tayyibi Ismailis, known as the Bohras in South Asia, were led by da'is (deputies of their hidden imams). This collection of studies represents the first scholarly attempt to conduct a comprehensive survey of the modern history of the two Ismaili branches since the mid-19th century. It covers a wide range of topics and issues related to the Nizari Ismailis, and a separate section is dedicated to the modern history of the Tayyibi Bohras and the developments within this community.