To summarize recent advances in the classification of preradiographic axial spondyloarthritis (SpA).Inflammation in the sacroiliac joints precedes radiographic damage that is necessary to establish a diagnosis of ankylosing spondylitis (AS). Preradiographic axial SpA refers to patients with SpA who exhibit signs and symptoms of axial involvement, but lack criteria for AS. Patients with axial SpA can have remarkably similar clinical features and disease activity as those with early AS. MRI is a sensitive method for detecting sacroiliac joint inflammation, which is useful in predicting the development of AS. Whole-body MRI has emerged as a means to visualize additional areas of involvement. However, it may be less sensitive than conventional MRI, and thus its added value will need to be further assessed. The incorporation of MRI evaluation of the sacroiliac joints and HLA-B27 testing into criteria for identifying individuals with preradiographic axial disease has led to the development of criteria for classifying axial SpA.The development of classification criteria for axial SpA will aid in the identification of patients suitable for clinical trials testing whether early intervention will slow the development and/or progression of structural changes in that lead to AS.