We adopt a definition of state capacity that focuses on policy implementation and propose to measure the construct by examining the proportion of total tax revenue from income taxes. We make three major contributions in this paper. First, unlike other scholars, we focus explicitly on income tax collection rather than looking at overall tax collection. Second, we demonstrate the construct validity of our measure. Third, we compare our measure to the most commonly used indicator for state capacity, tax/GDP, to demonstrate the construct validity of that measure and how ours performs better for our large sample of cases.