Medicaid policies vary over time in states with section 1115 demonstrations. Policy changes occur when a state first implements a demonstration, but many states also add or remove demonstration policies during a demonstration period via amendments. States also commonly change policies between an initial demonstration and its renewal. These policy changes over time present an opportunity for the evaluation of demonstrations and can also introduce complications that states and their independent evaluators need to address. This white paper discusses evaluation approaches for three categories of section 1115 demonstrations: demonstrations that add or change policies over time; demonstrations that introduce multiple individual policies at the same time; and demonstrations implemented in different parts of the state at different times.