Colorado manages water using an administrative structure that is unique among the United States following the doctrine of prior appropriation: Water rights are adjudicated not by the State Engineer, but by Water Courts – separate from and operating in parallel to the criminal and civil courts – established specifically for this purpose. Fundamental to this system is the notion that water rights are property, with consequent protections under the US Constitution, but with the significant constraint that changes in water rights must not injure other water rights, either more senior or more junior. Population growth and climate change will certainly trigger changes in water administration, to be guided by the recent Colorado Water Plan. To provide the foundation necessary to appreciate these changes, this paper reviews the history of Colorado water administration and summarizes the complementary roles of the Water Courts and the State Engineer. Understanding water administration in Colorado depends on a firm grasp on how these two branches of state government formulate and implement water policy.