An expanding range of biological therapies is available for patients with rheumatoid arthritis. Clinical trials and real-life experience demonstrate significant interpatient heterogeneity in efficacy as well as important adverse effects of these treatments. In order to maximise their benefit:risk ratios and to minimise later joint damage, we need to define predictors of response and, ideally, of adverse effects for each of these drugs. There is huge interest in this field of 'personalised medicine', which should allow us to optimally match patient with treatment, providing the parallel benefit of reduced treatment costs. In this short article the current state of the art for licensed biological therapies is summarised. There have been some noteworthy discoveries but the challenge is now to design studies to confirm and validate these findings while also devising large, potentially international, collaborations to identify additional, robust biomarkers that predict outcome.