This disclosure describes a state machine framework for programming closed-loop algorithms that control the delivery of therapy to a patient by an implantable medical device (IMD). The state machine framework may use one or more programmable state parameters to define at least part of a structure of a state machine that generates one or more therapy decisions based on one or more sensed states of the patient. The state machine framework may include a state machine runtime environment that executes on an IMD and that is configurable to implement a variety of different state machines depending on programmable state parameters that are received from an external device. The techniques of this disclosure may, in some cases, allow IMD developers and/or users to program, change, and/or download new closed-loop control policy algorithms during the lifespan of the IMD without requiring new firmware code to be downloaded onto the IMD.