The intrametropolitan relationship between municipality-level physical environment and crime changes appears to have been overlooked by crime and environment researchers. The current effort focuses on permeability; suggests dynamics whereby permeability affects changing municipality-level crime patterns across a metropolitan area; selects and operationalizes theoretically appropriate permeability indicators; and links permeability to unexpected crime changes. Data are from 355 municipalities in the Philadelphia metropolitan area, and property and violent crime unexpected changes over two change periods are assessed. Three municipality-level indices reflecting internal and boundary permeability are developed that are internally consistent and cross reference in sensible ways with large-scale physical environment features of municipalities. Permeability indicators link as predicted with unexpected violent and property crime changes. This research provides a theoretical and empirical foundation for linking permeability to changing municipality-level crime rates across a metropolitan area.