This observational study will target patients with axial spondyloarthritis (axSpA) and psoriatic arthritis (PsA) who have started treatment with bimekizumab, upadacitinib, risankizumab, guselkumab, or a tumour necrosis factor-alpha inhibitor (e.g., adalimumab or etanercept) at NHS hospitals in the United Kingdom. Information from patients' medical records will be collected, and patients will complete surveys about their experiences with their treatment. The study will look at treatment effectiveness from both healthcare professionals' and patients' points of view.

Patient experience surveys will be administered prospectively throughout the study period, whereas the review of patients' medical records will be conducted retrospectively towards the end of the study period.

Inclusion Criteria:

• Participant has a clinical diagnosis of axial spondyloarthritis (axSpA) or psoriatic arthritis (PsA).
• Participant has been prescribed advanced therapy within one month prior to enrolment in the study, to treat their axSpA or PsA.
• Participant is aged 18 years or older at enrolment.

Exclusion Criteria:

-Participation in a clinical trial at enrolment.

Participants will be selected from patients attending NHS hospitals and related healthcare sites targeted across the United Kingdom, including England, Scotland, Wales, and Northern Ireland. These sites are secondary and tertiary care centres where patients with axial spondyloarthritis or psoriatic arthritis are routinely managed by rheumatology services.

Individual participant data (IPD) from this study will not be shared with other researchers. In accordance with the study protocol and relevant data protection regulations, including GDPR, only aggregated data and summary results will be made available for scientific dissemination. All data provided will be fully anonymized and presented in aggregate form to ensure participant confidentiality and privacy. No individual-level data or information that could identify participants will be shared outside of the authorized study team.