Philosophers of criminal punishment widely agree that criminal punishment should be “proportional” to the “seriousness” of the offense. But this apparent consensus is only superficial, masking significant dissensus below the surface. Proposed proportionality principles differ on several distinct dimensions, including: (1) regarding which offense or offender properties determine offense “seriousness” and thus constitute a proportionality relatum; (2) regarding whether punishment is objectionably disproportionate only when excessively severe, or also when excessively lenient; and (3) regarding whether the principle can deliver absolute (“cardinal”) judgments, or only comparative (“ordinal”) ones. This essay proposes that these differences cannot be successfully adjudicated, and one candidate proportionality principle preferred over its rivals, in the abstract; a proportionality principle only makes sense as an integrated part of a more complete justificatory theory of criminal punishment. It then sketches a proportionality principle that best fits the responsibility-constrained pluralist theories of criminal punishment that currently predominate. The proportionality principle it favors provides that punishments should not be disproportionately severe, in noncomparative terms, relative to an agent’s culpability in relation to their wrongdoing