Certolizumab pegol (Cimzia®) is a polyethylene glycolylated antigen-binding fragment of a recombinant human monoclonal antibody that binds to and selectively neutralizes tumour necrosis factor (TNF) α. In the EU, subcutaneous certolizumab pegol is indicated for the treatment of adults with severe active axial spondyloarthritis (axSpA), comprising ankylosing spondylitis (AS) and non-radiographic axSpA (nr-axSpA), and for adults with active psoriatic arthritis (PsA). In the USA it is indicated for the treatment of adults with active AS or active PsA. This article reviews the efficacy and tolerability of certolizumab pegol in these patients and briefly summarizes its pharmacology. In two ongoing, well-designed studies, data at 12 and 24 weeks showed that treatment with certolizumab pegol (200 mg every 2 weeks or 400 mg every 4 weeks) was effective in improving the clinical signs and symptoms of disease, health-related quality of life and productivity in patients with axSpA (the RAPID-axSpA study) or PsA (the RAPID-PsA study), with the improvements maintained during longer-term (48 weeks) treatment. Within the axSpA population, clinical benefits with certolizumab pegol were seen both in patients with AS and in those with nr-axSpA. In addition, 12 weeks’ treatment with certolizumab pegol reduced inflammation in the sacroiliac joints and spine in patients with axSpA and 24 weeks’ treatment with the agent slowed radiographic disease progression in patients with PsA. Certolizumab pegol was generally well tolerated in these studies, with a tolerability profile consistent with that seen in previous clinical trials in other indications. Although additional long-term and comparative data are needed to position certolizumab pegol with respect to other TNFα antagonists, current evidence indicates that certolizumab pegol is an effective option for the treatment of axSpA (including AS and nr-axSpA) and PsA.