An outstanding feature of the early modern Indian Ocean World is the large number of women who exercised formal sovereign political power. Based on a systematic survey of 277 queens regnant in the Indian Ocean World from the fourteenth to the nineteenth century, this article discusses four possible explanations for the relative frequency of female rule: religion, trade, political stability, and gender relations. It concludes that the spread of world religions, particularly Islam, entailed a decrease in the acceptance of female rule in large parts of the region, although its influence varied, and, in sharp contrast to the Middle East, many Muslim polities in the Indian Ocean World were at one time or another during the period under study led by a woman. The notion that women rulers were preferred because of their commercial skills and ability to promote peaceful, open, and trade-friendly policies is rejected as a causal explanation because of its weak support in contemporary sources. The relative frequency of female rule in the Indian Ocean World can instead be explained on a general level by a combination of the desire for political and dynastic stability and the matrifocal orientation of many societies along the Indian Ocean rim. However, as in Europe during the same period, female rule tended mainly to be adopted as a last resort, and female royal power tended, apart from a few exceptions, to be weak and short-lived.