Proportionality has been used as an analytical method in the constitutional jurisprudence of courts around the world, including in Australia. The method has not, however, been free from controversy. Since its first introduction into Australian constitutional law, there have been debates regarding the appropriateness of proportionality testing in this context. To date, these debates have been lacking in one important respect: they have not been sufficiently grounded in theory. In times when the global literature on the subject was relatively nascent and applications in comparative constitutional contexts sparse, the under-theorisation of Australian proportionality was understandable. This is no longer the case. The burgeoning international literature and jurisprudence in this field has in recent years generated a rich body of judicial and academic thought from which to elicit a properly theorised consideration of proportionality. Drawing on these resources, this thesis proposes a theoretical framework for proportionality. It uses this framework to explore a key question in the Australian context: when is proportionality an appropriate analytical tool in constitutional jurisprudence? In examining this question, the thesis considers the primary concerns regarding the appropriateness of proportionality in Australian constitutional law and how these might be addressed. It also makes principled suggestions for the development of Australian doctrine.