The diamondback terrapin has been considered a keystone species along its range in the coastal, brackish estuaries bordering the Atlantic Coast and Gulf of Mexico. Historically, diamondback terrapin populations have been numerous; however, in Alabama; the population has dramatically declined over the past century due to a variety of threats. The threats in Alabama include predation by raccoons, incidental drowning in crab traps, as well as road mitigated mortality. Because of these threats, collaboration efforts between UAB, USA, DISL, and the Alabama Department of Conservation and Natural Resources, a head-start program has been initiated to mitigate the predation of hatchlings. As such, the diamondback terrapin head-start program provides a unique situation to evaluate the biology, ecology, and conservation of hatchling and post-hatchling diamondback terrapin. Studies involving the head-start program include evaluating maternal investment in eggs and offspring, growth patterns of offspring, evaluation of carapace shape as an accurate sexing method for immature terrapin, fitness assays, and feeding assays. By understanding the diamondback terrapin in the lab, we can better benefit their survival in the wild. This thesis includes a series of studies related to the biology and conservation of the diamondback terrapin. Chapter 1 investigates maternal investment in offspring and the impact of incubation temperature on offspring relative to egg size, hatchling size, and growth. Chapter 2 evaluates a potential sexing technique for hatchling and immature terrapin based on carapace morphology, and Chapter 3 examines two aspects of fitness of head-start terrapin (righting response and ability to adapt to a live food source).