Journal article: We build a model in which both illegal immigration and the size of the informal sector are endogenously determined. In this framework, we show that indirect policy measures such as tax reduction and detection of informal activities can be used as substitutes for border enforcement, in order to counteract illegal immigration. We also find that a welfare-maximizing government will set the tax rate to a lower value, if it includes illegal immigration in its objective function, instead of focusing on the well-being of native workers only.