Inclusion Criteria:  Informed consent/assent obtained before any study-related activities. Study-related activities are any procedures that are carried out as part of the study, including activities to determine suitability for the study. Diagnosis of congenital severe haemophilia A (FVIII below 1%) or moderate/severe congenital haemophilia B (FIX (coagulation factor IX) below or equal to 2%), or congenital haemophilia with inhibitors. For arm 1 only: Male aged below 12 years of age at the time of signing informed consent.  For arm 1 only: Patients with medical records of a total of at least 26 weeks of treatment within the last 52 weeks prior to enrolment (For patients that have been diagnosed with haemophilia below 1 year prior to enrolment, historical medical records from time of diagnosis will suffice as long as medical records of a total of at least 26 weeks of relevant treatment is available)  Patients with HAwI (haemophilia A with inhibitors) with medical records of a total of at least 26 weeks of on demand treatment within the last 52 weeks prior to enrolment. Patients with HBwI (haemophilia B with inhibitors) with medical records of a total of at least 26 weeks of on demand treatment within the last 52 weeks prior to enrolment Patients with HBwI regardless of the regimen and duration of previous haemophilia treatment Patients without inhibitors with medical records of a total of at least 26 weeks of PPX (prophylaxis) treatment within the last 52 weeks prior to enrolment For arm 2 only: Male patients (regardless of age) previously treated with concizumab via compassionate use.  Exclusion Criteria:  Known or suspected hypersensitivity to study intervention or related products. Known inherited or acquired coagulation disorder other than congenital haemophilia. Ongoing or planned Immune Tolerance Induction treatment. History of thromboembolic disease (aIncludes arterial and venous thrombosis including myocardial infarction, pulmonary embolism, cerebral infarction/thrombosis, deep vein thrombosis, other clinically significant thromboembolic events and peripheral artery occlusion.). Current clinical signs of or treatment for thromboembolic disease. Patients who in the judgement of the investigator are considered at high risk of thromboembolic events (Thromboembolic risk factors could include, but are not limited to, hypercholesterolemia, diabetes mellitus, hypertension, obesity, smoking, family history of thromboembolic events, arteriosclerosis, other conditions associated with increased risk of thromboembolic events).