This paper introduces MiniCP, a lightweight, open-source solver for constraint programming. MiniCP is motivated by educational purposes and the desire to provide the core implementation of a constraint-programming solver for students in computer science and industrial engineering. The design of MiniCP provides a one-to-one mapping between the theoretical and implementation concepts and its compositional abstractions favor extensibility and flexibility. MiniCP obviously does not support all available constraint-programming features and implementation techniques, but these could be implemented as future extensions or exploratory projects. MiniCP also comes with a full set of exercises, unit tests, and development projects.