At OMERACT 8 in May 2006 in Malta, the International Classification of Functioning, Disability and Health (ICF) was introduced as a universal model and a universal classification to describe human functioning. The potential usefulness of the ICF for the OMERACT process was highlighted and reported in a position paper following the OMERACT 8 meeting. Since then representatives of several OMERACT working groups with an interest in the ICF joined an OMERACT-ICF reference group. Most members had experience with the ICF and worked further to integrate the ICF into OMERACT. We describe the main roles of the ICF in the OMERACT process and the challenges when practice confronts theory.