RNA interference has been of great interest not only as a research tool to suppress gene expression but also as an emerging therapeutic strategy to silence disease genes. However, the therapeutic use of siRNA faces the in vivo delivery challenge. An alternative method that could potentially be used for siRNA delivery into primary immune cells for therapeutic purposes is an ex vivo route, whereby immune cells could be isolated from a patient, reprogrammed with siRNAs, and infused back into the same patient. This chapter describes siRNA delivery into human primary monocytes and dendritic cells using a standard electroporation technique. Dendritic cells occupy a central role in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the generation of protective CD8+ T cell immunity.