This chapter is devoted to programming, which is the creation of programs that prescribe systems. Therefore, Sect. 5.1 considers the connection between a program and its prescribed system. This means we discuss the semantics of descriptions related to snapshots and executions. We consider two main ways towards execution of a description, namely, compilation and interpretation. Section 5.2 explains how programming is used to develop new systems or new parts of existing systems without having a physical referent system as a basis. In Sect. 5.3, we look into the details of how the model descriptions as discussed in Chap. 4 are programmed. We look into the correctness of programming in Sect. 5.4, which is closely related to the correctness of models as discussed in Sect. 3.2. Finally, we explain where to find extra companion resources for this book in Sect. 5.5.