The purpose of this study is to evaluate safety, effiectiveness, and to gain insight into the treatment experience of participants prescribed BRIUMVI® (ublituximab-xiiy) in the real-world setting

Inclusion Criteria:

1. Confirmed Multiple Sclerosis (MS) diagnosis.
2. Participants who have not received any BRIUMVI® (ublituximab-xiiy) infusion prior to study start. Participants who have been prescribed BRIUMVI® (ublituximab-xiiy) but have not yet received their first infusion on Day 1 of 150 milligrams (mg) can be included.

Exclusion Criteria:

1. Have received any live or live-attenuated vaccines (including for varicella-zoster virus or measles) within 4 weeks prior to first BRIUMVI® (ublituximab-xiiy) administration or any non-live vaccines within 2 weeks prior to first BRIUMVI® (ublituximab-xiiy) administration.
2. Any active infection (e.g., active Hepatitis B virus [HBV])
3. Concurrent participation in any interventional MS trials, or planned concurrent treatment with other Multiple Sclerosis Disease Modifying Therapy (MS DMT) during the study period.

The study population will include participants with RMS who are receiving BRIUMVI® (ublituximab-xiiy).