There are two important requirements that any approach to formalizing Design patterns must meet. First, the approach must enable the precise specification of the implementation requirements and behavioral guarantees associated with a wide range of patterns. Second, the formalization of each pattern must retain the pattern’s inherent flexibility. In this chapter, we present a novel approach to formalizing Design patterns that satisfies these seemingly conflicting requirements. For the formalism to be of practical value, we also need tools that can assist practitioners in determining whether the patterns used in designing their systems have been implemented correctly. Such tools are especially important during system maintenance and evolution to ensure that the design integrity of a system is not compromised. We show how our approach lends itself to the construction of such tools.