The use of biological agents in the treatment of rheumatoid arthritis (RA) has grown constantly since the approval of the first therapeutic monoclonal antibody against tumor necrosis factor-alpha (TNF) in 1996. While these agents transformed RA treatment, not all patients respond to these agents. Moreover, the cost of these agents is high, and some patients may suffer from adverse events. Thus, the prediction of individual response to biological treatment has become a major clinical challenge in RA. Recent studies have provided evidence that biomarkers may be identified predictive of the response to therapy with these agents. This article will review some of the recent advances in the biomarkers and therapeutic drug monitoring as predictors of response to TNF inhibitor therapies in patients with RA.