This thesis is about rainmaking amongst the Ihanzu (or Isanzu), a 30,000-strong matrilineal, Bantu-speaking agricultural group of north-central Tanzania. By examining rain rituals and their cosmological underpinnings as locally envisaged, I suggest that central to the Ihanzu cultural imagination lies the notion of gender complementarity. In a number of contexts, but particularly in the context of rainmaking, I show how masculine and feminine principles of a gendered universe, when combined, are seen as a site of cosmic and divine powers. To join the genders is to transform, to create, to rejuvenate. Using oral and archival sources, the first section examines the nature of the Ihanzu dual monarchy between 1885 and 1976. In spite of the radical political, economic and social changes that took place throughout this period, the dual leadership-with one male and one female-and people's understandings of royal power and legitimacy remained constant: control over rains is control over reigns. Section two examines annual rainmaking rites as they occur today. The point is to show the extent to which gender complementarity pervades these rites, and the local logic as to why this must be so. An indigenously grounded, gendered model of transformation is developed that applies equally to making children as to making rain. Power, in Ihanzu eyes, comes in gendered pairs. Section three discusses measures taken when annual rain rites fail to bring rain, and how the gendered model of transformation applies to these remedial rites. The penultimate chapter, on rain-witchcraft, suggests that gendered witches are a cosmological inversion of gendered rulers, yet for both duos their powers are based on gender complementarity. In the conclusion it is argued that the notion of gendered complementarity as developed in the thesis might be equally useful in explaining rain rites elsewhere in Africa.