• Patients with a confirmed diagnosis of primary CSU by the treating physician.

• Aged at least 18 years on the date of enrolment.

• Written informed consent of the patient to participate in the study (according to country specifications) and willingness to complete full follow-up period of 24 months.

• Cohort-specific observational inclusion criteria:

‣ Cohort 1: Inadequate control of CSU despite licensed dose of sgH1-AH (no other pre-treatments permitted) and decision (independent of study enrolment) to escalate sgH1-AH treatment.

⁃ Cohort 2: Inadequate control of CSU despite licensed dose or escalated sgH1-AH(s) (no other pre-treatment with exception of first generation H1-AH permitted) with decision (independent of study enrolment) to switch to remibrutinib treatment as per local label.

⁃ Cohort 3: Any other treatment received in addition to H1-AH, any time during patients' CSU treatment history, with decision (independent of study enrolment) to switch to remibrutinib treatment as per local label. Note, occasional steroid rescue medication is out of scope for cohort definition. If a patient had been on continuous steroids for at least three weeks during treatment history, they will be included in cohort 3.

∙ Note: Candidate patients must not have initiated the next escalated treatment step (i.e. up dosed AH for cohort 1, or remibrutinib for cohorts 2 and 3) prior to their enrolment to ensure the baseline visit captures their clinical status before treatment escalation.