This article proposes a theory of Prosodic Domain Circumscription, by means of which rules sensitive to morphological domain may be restricted to a prosodically characterized (sub-)domain in a word or stem. The theory is illustrated primarily by a comprehensive analysis of the Arabic broken plural; it is further supported by analysis of a number of processes from other languages, yielding a formal typology of domain-circumscription effects. The results obtained here depend on, and therefore confirm, two central principles of Prosodic Morphology: (1) the Prosodic Morphology Hypothesis, which requires that templates be expressed in prosodic, not segmental terms; and (2) the Template Satisfaction Condition, which requires that all elements in templates are satisfied obligatorily.