One of the most effective forms of plant defense against viruses is posttranscriptional gene silencing (PTGS). This process implies that a virus can trigger the host plant's RNA-silencing machinery and ultimately become the target of RNA silencing. PTGS is, therefore, an attractive endogenous process that can be exploited to study gene function. One of the most efficient approaches of initiating PTGS is through virus-induced gene silencing (VIGS). When a recombinant viral vector (VIGS vector), carrying a host-derived target gene sequence, infects a plant, viral double-stranded RNAs are synthesized leading to the activation of the antiviral RNA silencing pathway and the subsequent knockdown of the endogenous host gene. VIGS is both a powerful reverse and forward genetics tool and is amendable to high-throughput genetic screens and functional genomics. Here, we describe the use of tobacco rattle virus-based VIGS techniques to study gene function in Nicotiana benthamiana, tomato, and Arabidopsis thaliana.