The morphogenetic events that occur during fetal development of the mammalian ovary are crucial to the establishment of adult female fertility. While our knowledge of the cellular and molecular aspects of ovary development is increasing, the structural rearrangements that give rise to the cortex and medulla and the relation of other female reproductive tissues to the ovary have not been thoroughly investigated. In this study, we used tissue clearing and lightsheet microscopy to investigate the stepwise morphogenesis of the ovary. We found that the ovary transitioned from an elongated to a crescent-shaped structure, suggestive of a folding mechanism. As this occured, the ovarian surface epithelium wrapped from the ventral to the dorsal side of the ovary, forming the ovarian cortex and engulfing the dorsal face of the ovary to form the medulla. To identify the tissue mechanics that drive ovary folding, we investigated proximate tissues closely associated with the ovary including the M&uumlllerian duct, the cranial suspensory ligament, and the rete ovarii. We found that relocation of the M&uumlllerian duct to the ventral aspect of the ovary was associated with expansion of mesonephric tissue that left the ovary fully encapsulated by birth. The cranial suspensory ligament, which tethers the ovary to the body wall and to the M&uumlllerian duct may exert mechanical tension that triggers ovarian folding. Finally, we found that the rete ovarii, a previously dismissed epithelial appendage of the ovary, significantly expanded during late gestation and may act to anchor the ovary to the mesonephros, leading to integration of extrinsic components into the ovarian medulla. This detailed atlas of ovary morphogenesis reveals novel relationships among the ovary and its surrounding tissues and paves the way towards the functional investigation of the relationship between architecture and differentiation of the mammalian ovary.