This article examines the assignment of functional responsibilities to municipalities, contributing conceptualization and measurement for the analysis of breadth of those responsibilities across the American states. It also investigates determinants of functional breadth: alternative explanations are explored in an analysis of municipalities in metropolitan areas. Using data from the 2012 Census of Governments, two measures of functional breadth are reported, thus evaluating the reliability of the findings across alternative measurements of breadth. The main findings are that a diverse scope of functional responsibilities is prevalent across American municipalities and that the institutional environment of municipalities influences those diverse functional responsibilities. Additional findings are that certain factors differentially affect the scope of service responsibilities, according to a quantile analysis of the dependent variable’s distribution. Although its primary contribution is to the literature on functional responsibilities of governments, the article also proposes a political market approach to identify factors influencing functional responsibilities.