A high level of taxation, a cumbersome legislation, high payroll taxes and labor costs are only some of the many factors which may push firms into informality. Among these factors, the availability of credit and its cost have received little attention. In this paper we study how the choice to operate underground (and to what extent) interacts with financial development. As in Ellul et al. (2012), the starting point of our analysis is that the ability to reveal and signal revenues reduces information frictions and the cost of credit. When
firms or individuals operate underground their ability to signal revenues and assets is lower, and the cost of credit higher. As financial markets develop, more efficient intermediaries enter the market and the cost of credit falls, increasing the opportunity cost of continuing to operate underground. In short, financial market development is negatively correlated with the size of the underground economy.