Certolizumab pegol (Cimzia(®)) is currently the only PEGylated anti-TNFα biologic approved for the treatment of rheumatoid arthritis and Crohn disease. The product, developed by UCB, is a humanized antigen-binding fragment (Fab') of a monoclonal antibody that has been conjugated to polyethylene glycol. Certolizumab pegol was approved as a treatment for rheumatoid arthritis in the EU, US and Canada in 2009, and as a treatment for Crohn disease in Switzerland in 2007 and the US in 2008. Certolizumab pegol is entering into an increasingly competitive marketplace, especially in rheumatoid arthritis, but clinical data demonstrate benefits across a range of clinical, radiographic and patient reported outcomes.