Existing literature suggests that either colonial settlement conditions or the identity of colonizer were influential in shaping the post-colonial institutional environment, which in turn has impacted long-run economic development. These two potential identification strategies have been treated as substitutes. We argue that the two factors should instead be treated as complementary and develop an alternative and unified IV approach that simultaneously accounts for both settlement conditions and colonizer identity to estimate the potential causal impact of a broad cluster of economic institutions on log real GDP per capita for a sample of former colonies. Using population density in 1500 as a proxy for settlement conditions, we find that the impact of settlement conditions on institutional development is much stronger among former British colonies than colonies of the other major European colonizers. Conditioning on several geographic factors and ethno-linguistic fractionalization, our baseline 2SLS estimates suggest that a standard deviation increase in economic institutions is associated with a three-fourth standard deviation increase in economic development. Our results are robust to a number of additional control variables, country subsample exclusions, and alternative measures of institutions, GDP, and colonizer classifications. We also find evidence that geography exerts both an indirect and direct effect on economic development.