The discovery of RNAi, in which double-stranded RNA (dsRNA) suppresses the translation of homologous mRNA, has had a huge impact on evolutionary genetics by enabling the analysis of loss-of-function phenotypes in organisms in which classical genetic analysis is laborious or impossible. In this chapter, we discuss an RNAi method via simple dsRNA injection in the red flour beetle, Tribolium castaneum . Tribolium is gaining popularity in evolutionary genetics due in part to the ease of RNAi application. We describe procedures for dsRNA synthesis and injection and provide a description of the injection apparatus. In addition, we detail two methods to validate the efficacy of RNAi (real-time PCR and western blot analyses). Although this chapter focuses mainly on Tribolium , many of the molecular biology and injection procedures described here are applicable to other organisms with some modifications. A few notes regarding dsRNA injection in other species are also included.