This is a European prospective noninterventional cohort study in patients with axial spondyloarthritis (axSpA) (including both ankylosing spondylitis (AS) and nonradiographic axial spondyloarthritis (nr-axSpA)) being treated with certolizumab pegol (CZP). The overall duration of observation per patient will be 12 months (52 weeks). The primary objective of this NIS is to assess the effectiveness of CZP in patients with axSpA (AS and nr-axSpA) under routine clinical practice in Europe. The primary measure of the effectiveness of CZP will be the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI);
The primary variable is change from Baseline in BASDAI to Week 52 in the overall axSpA population, and the AS and nr-axSpA subpopulations. Other measures of effectiveness will be considered as secondary and other variables.