⁃ Main study:

• Have a confirmed diagnosis of PsA as determined by a rheumatologist with reference to Classification criteria for Psoriatic Arthritis (CASPAR)

• Start guselkumab or any approved interleukin-17 inhibitor (IL-17i) as a first, second, third, or fourth line of biologic disease-modifying antirheumatic drugs (bDMARD) therapy for the indication of PsA as part of standard clinical practice (according to local label, local regulations, and/or reimbursement requirements) at the time of enrollment into the observational study or within a maximum of 2 months after the initial baseline visit or after repeated baseline data collection

• Sign a participation agreement/Informed consent form (ICF) allowing data collection and source data verification in accordance with local requirements

• Able to read, understand, and intend to comply with completion of all Electronic patient-reported outcome (ePRO) instruments

• The treatment decision must be taken by the participating rheumatologist prior to, and independently of the participant's inclusion into the study, following clinical practice in accordance with local and overarching guidelines and local regulations

⁃ Substudy:

• Must sign the substudy ICF allowing data collection in accordance with local requirements

• Is scheduled to receive guselkumab or IL-17i, per routine clinical practice, in the main study

• Currently using or is willing to use wearables and/or commercial applications to track their disease within the course of their normal daily activities