The principle of legality has in recent years become an increasingly important tool of statutory interpretation. Despite its prominence, it has, I will argue, been applied inconsistently. This article examines two methodological difficulties in the application of the principle: its interaction with the doctrine of purposive construction, and its application to legislation cast in linguistically clear but broad terms. This analysis suggests that Australian courts are applying the principle in different ways without acknowledging emerging doctrinal differences. The last part of the article examines a series of contextual factors which courts have suggested may affect the strength of the presumption, but concludes that these have very limited explanatory or predictive value when charted against the methodological differences discussed earlier.