In this paper I propose a theory of meter that treats meter as Optimality-Theoretic (OT) faithfulness. At the core of the proposal is the notion of meter as similarity between an abstract metrical template consisting of prosodic structure without segmental content, and the prosodic structure of a line of verse. Faithfulness is the measure of similarity in OT. I develop a general theory of faithfulness between prosodic structures using standard OT tools, and apply it to meter. I test the theory by investigating two aspects of English iambic meters, phrasal peaks in weak positions, and stressed syllables in weak positions. Because many analytically interesting aspects of meter involve gradient preference rather than absolute metricality, the theory is embedded in the multiple-grammars theory of variation. The chief advantage of the present approach is its commitment to the grounding hypothesis, viz. the claim that rule-governed aspects of meter can be analyzed using the same tools as ordinary grammar.