Ranging from Cape Cod to nearly the Texas-Mexico border, the diamondback terrapin (Malaclemys terrapin) is the only species of North American turtle restricted to estuarine systems. Despite this extensive distribution, its zone of occurrence is very linear, and in places fragmented, resulting in a relatively small total area of occupancy. On a global scale, excluding marine species, few turtles even venture into brackish water on a regular basis, and only two Asian species approach the North American terrapin's dependency on estuarine habitats. Here we describe some of the biological and behavioral adaptations of terrapins that allow them to live in the rather harsh estuarine environment. In this chapter we review the natural and cultural history of this turtle, discuss conservation issues, and provide information on the types of research needed to make sound management decisions for terrapin populations in peril.