Adaptive systems are difficult to describe, difficult to investigate and extremely difficult to compare. In his seminal investigation of adaptive systems Holland proposed an adaptive
systems formalism specifically to address these concerns. This straightforward formalism may be used as a general framework for describing and investigating adaptive systems and examples of both of these cases are discussed. This work promotes the adoption of the formalism in the field of artificial immune systems and provides the immunological example of the clonal selection theory ‘adaptive plan’.