In order to measure disease activity, progression and response to therapy, it is important to use accurate, reliable and feasible outcome measures that can ideally be used in longitudinal cohorts, clinical trials and clinical practice. With emerging therapies, the focus on the methodology of outcome assessment has increased to ensure that discriminant and responsive instruments are used. This chapter reviews available measures of three major areas of disease impact in the spondyloarthropathies (disease activity, structural damage and functioning) and discusses the relevance for use in clinical practice. First, the outcome measures available for the assessment of different domains in ankylosing spondylitis, composite-indices and response criteria for use in clinical trials and clinical practice in ankylosing spondylitis are discussed. Secondly, the performance of these in psoriatic arthritis and more disease-specific instruments in psoriatic arthritis are discussed.