Chapter 1. In the United States, building infrastructure is primarily the responsibility of municipal governments. However, prior empirical evidence suggests these governments are borrowing-constrained. This paper provides new evidence and theory that link the constraint to the dominance of retail investors in the municipal bond market, who pay less attention to new bond issues than more specialized investors, such as municipal mutual funds. Supporting this hypothesis, I find that the mutual funds disproportionately buy newly issued bonds and gradually resell them to other investors. Furthermore, a 1% inflow to the mutual fund sector increases bond issuance by county governments by 0.2% and reduces the interest rate by 0.2 basis points in t...