This study aims to evaluate the use of rivaroxaban and its short term safety when used by patients for the new indications of prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation, treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE) and prevention of recurrent DVT and PE. Any adult patient started by their care team on rivaroxaban or an alternative anticoagulant for the specified indications during the study period will be eligible to take part. A questionnaire will be completed by the care team of each patient at the start of treatment and again 12 weeks later. The care team will complete the questionnaires using information from the patient's medical notes, not by asking the patient directly. If a participant has an adverse event during the 12 week period, we may ask the patient's care team to fill out a further follow up questionnaire. No other examinations or tests will be performed. Patients will only be recruited to the study after the clinical decision to prescribe rivaroxaban or an alternative anticoagulant has been made, so that prescribing behaviour is not altered by the study. It is an observational, non-interventional study covering the whole of England and Wales.