Magnetic resonance imaging (MRI) has been recently introduced as a classification criterion for spondyloarthropathies in the Assessment of Spondylarthritis International Society criteria. Therefore, it plays an increasingly important role in the diagnostic workup of spondyloarthropathies. In this article, we will review the MRI imaging features of axial spondyloarthritis from sacroiliitis to spine abnormalities; we will explain the rationale for MRI imaging, the evidence for whole body MRI, and we will approach the use of MRI for monitoring treatment response.