Rheumatoid arthritis (RA) is a chronic inflammatory disease that involves synovial tissue and leads to joint destruction. There are currently 5 tumor necrosis factor (TNF) antagonists licensed for the treatment of RA. This review summarizes the predictors of response to TNF antagonists in RA. Demographic variables were found to predict response, although not consistently. The variables associated with poor clinical response were presence of radiographic joint erosions at baseline, poor functional capacity at baseline, presence of human antibodies against TNF chimeric antibodies, and increase in anti-DNA and antinuclear antibodies. In selected populations, polymorphisms of TNF, TNF receptor, and Fc γ receptor were related to clinical response. Expression of TNF and other inflammatory cytokines in synovial tissue was explored. The heterogeneity of study populations limits the generalizability of the results in most studies.