RNA interference (RNAi) is a conserved sequence-specific gene silencing mechanism that is induced by double-stranded RNA (dsRNA). The development of methods that allow internalization of dsRNA and concomitant silencing of the desired gene has not stopped since the first demonstration of RNAi in Caenorhabditis elegans . In this chapter, we describe how to introduce exogenous dsRNA into adult Drosophila in order to interfere with endogenous or viral gene expression.