The purpose of this study is to define cut-off values of the most widely used composite scores and patient-reported outcomes, for levels corresponding to remission/low disease activity and for changes in levels corresponding to flares, in PsA, when remission/low disease activity and flare are defined from the patient and physician perspective. The ReFlaP (Remission/Flare in PsA) study is a prospective, multicentric international, longitudinal, observational study.