Architectural change heuristics are a very powerful mechanism for implementing architectural optimisation. They allow for both the capture of the systematic changes required to maintain system integrity and the often poorly understood rationale of expert knowledge. However, even though heuristics are one of the oldest and most widely used problem-solving mechanisms, they are also perhaps one of the most mis-used and ill-defined. In order to understand how heuristics can be used in optimising system architectures it is important to understand the nature of heuristics especially as they apply to architectural optimisation. This paper presents a framework that can be used to categorise and classify heuristics as they are used in system optimisation. It is anticipated that this framework will provide a common foundation within which to discuss heuristics in architectural optimisation.