This is a prospective, non-interventional study in patients with CSU where the treatment decision prior enrolment has been made to either escalate current sgH1-AHs treatment or escalate/switch current treatment to remibrutinib. The primary aim of this study is to gather real-world effectiveness and safety data for remibrutinib, covering a broader, real-world clinical practice population. This local US study is part of an umbrella design which brings the evidence needs from multiple countries under the REASSERT global program (CLOU064A2402).