Silencing specific gene expression by RNA interference (RNAi) has rapidly become a standard tool for the reverse genetic analysis of gene functions. It also has tremendous potential for managing diseases for which effective treatment is currently unavailable or suboptimal. However, the poor cellular uptake of synthetic small interfering RNAs (siRNAs) is a major impediment for their clinical use. Great progress has been made in recent years to overcome this barrier, and several methods have been described for the in vivo delivery of siRNA. Moreover, the latest advances have focused on achieving targeted siRNA delivery restricted to relevant tissues and cell types in vivo. These approaches are expected to reduce the dose requirement as well as minimize siRNA-induced toxicities, thereby advancing the field of siRNA therapy towards clinical use.