This chapter addresses the relation between principles, balancing, and proportionality. First, it provides an overview of the most relevant views of the nature and role of principles in the law. Then it presents the different ways in which those views account for the application of principles, with a focus on balancing, as a way of reasoning and arguing with principles. On this basis, the chapter sheds light on the connection between balancing and the idea of proportionality, which plays a central role in contemporary law. The analysis is structured as follows. Section 1 presents the different accounts of the nature and structure of principles emerging from the reflection on this type of legal standards, in relation to the nature and role of legal rules. Section 2 examines how these accounts of principles address their application and the relevance of the idea of balancing in that respect. Section 3 addresses the relationship between balancing and the standard of proportionality, and the terms in which this relation serves as the basis of a doctrine of proportionality that lies at the core of the contemporary legal discourse. Section 4, then, presents the most influential versions of this doctrine – the standard version – and its variants, to outline the new directions in which the theory of proportionality is developing and highlight that the idea of proportionality is apt to guide institutional action beyond the domains in which it has been applied so far.