This article discusses the major scholarly developments in the study of Ismaili Muslim history and thought. Scholarship on the Ismailis, the second largest branch of Shi‘i Islam, once relied on hostile depictions produced by their adversaries. With the recovery of more primary sources over the last several decades, Ismaili studies is now progressing at a rapid pace. The Ismaili movement originated from a schism in the Imami Shi‘i community over the succession to Ja‘far al‐Sadiq, the fifth Shi‘i Imam. The Ismailis upheld the succession rights of al‐Sadiq's son and designated heir, Isma‘il, and his lineal descendants. The earliest Ismailis directed a revolutionary da‘wah in the ninth century and established the Fatimid Caliphate (909‐1171). Ismaili doctrine during these periods evolved from a gnostic cosmology into a Neoplatonic metaphysics. It also featured cyclical conceptions of Prophethood and Imamat and stressed the distinction between the exoteric (zahir) and esoteric (batin) dimensions of Islam. Major scholarly debates and thematic areas in the study of the pre‐Fatimid and Fatimid periods of Ismaili history pertain to the doctrinal character of early Imami Shi‘ism, Ismaili historiography, the origins of the earliest Ismailis, the emergence of the Ismaili da‘wah, the earliest Ismaili conceptions of Imamat, the different facets of Fatimid rule, the genealogy of the Fatimid Imam‐Caliphs, and the philosophical dimensions of Fatimid Ismaili thought.