RNA interference (RNAi) is currently the only method available in planaria for assessing the function of particular genes. We describe here a method for performing body-wide gene knockdown, relying on dsRNA production in bacteria and subsequent delivery to planaria by feeding a liver-bacteria mixture. This method is ideal for screening many genes in parallel, in a cost-effective and reliable manner. We also describe a ligation-independent cloning strategy, which is used to rapidly transfer single genes into an RNAi vector that is also appropriate for downstream applications such as in situ hybridizations. Together, these protocols represent useful components of the current planarian molecular tool kit.