This research study is seeking participants who have hemophilia B and need regular preventive treatment with factor IX protein (FIX) replacement therapy to prevent and also control bleeding events. To join the study , you must be male as assigned at birth, and between the ages of 16 and 65 years at the time of signing the informed consent form. The purpose of this study is to gather at least 6 months of information on bleeding events for each individual participant while they continue to use their usual FIX replacement therapy. There is no experimental drug or treatment being tested in this study. The study is informational, and part of a larger program to understand and treat hemophilia B with a potential experimental new therapy in the future. After participants complete this research study, should they be interested and eligible, they may be offered the opportunity to take part in a future study with this new therapy. There is no obligation to agree to taking part in this future study.