&NA;Genes are composed of deoxyribonucleic acid (DNA), the hereditary material of all nucleated cells. One way in which genes function is to direct the synthesis of specific proteins. When a gene is transferred to and expressed within a cell, the recipient cell produces the protein encoded by the transferred gene. This process forms the basis for gene therapy, which can be defined as the transfer of genes to patients for therapeutic purposes. Both genetic and acquired disorders may be treated, or even cured, by gene therapy. Potential orthopaedic applications include the treatment of arthritis, tumors, osteoporosis, and genetic diseases such as osteogenesis imperfecta, as well as the enhancement of tissue repair and regeneration. Impressive preclinical progress has been made in several of these areas. A phase I clinical trial of gene therapy for rheumatoid arthritis has just been completed. Orthopaedic gene therapy should become a clinical reality during the next decade.