The structure of ownership is recognized as a key factor for economic and social development. The traditional approach suggests that new property rights emerge when it becomes profitable to invest in their production. I extend this idea by arguing that simply defining new property rules is not enough for new rights to develop effectively, and that enforcement of those rules is just as important. Identifying and implementing an optimal combination of definition and enforcement activities then becomes the central issue in the development of property rights. I illustrate the application of this theory with a detailed study of the evolution of water rights in pre-modern Bohemia.