In this chapter, we've investigated one of the original reasoning architectures in artificial intelligence, the rules-based system. We focused specifically on forward chaining architectures with an implementation of a simple deduction system. Even though simple, this implementation can be used in a variety of settings, including embedding it within other systems with consequent hooks for manipulating the environment. We looked not only at a classical example from [Winston 93] (the ZOOKEEPER rule-set), but also at a simple fault tolerance example, managing sensors within an environment with reliability requirements. While rules-based systems do have their drawbacks, they provide a powerful architecture for reasoning in systems that interact with a user (such as classical diagnostics systems) down to embedded systems that must manage their environment.