INTRODUCTIONEfficient transfer and sustained expression of transgenes are among the most important issues in gene delivery. The majority of hematopoietic cells are nondividing or slowly self-renewing. Thus, they are refractory to most nonviral or retroviral delivery methods. Lentiviral vectors are capable of transducing nondividing cells and maintaining long-term and sustained expression of the transgenes. They are becoming useful for many delivery protocols, such as long-term expression of short hairpin RNA (shRNA) and functional genetics. They may also have great potential in gene therapy. This protocol describes lentivirus-vector-based delivery of foreign genes to hematopoietic cells. The method is applicable to various cell types in experiments that require long-term transgene expression.