Fibrinogen is a soluble protein, which circulates at high concentrations in our blood and plays different roles in wound healing and inflammatory processes. Factors that influence the function of fibrinogen may lead to excessive bleeding or hypercoagulability. Among these factors are mutations in the fibrinogen genes FGA, FGB, FGG which are the cause of rare fibrinogen disorders and interfere with fibrinogen function (Afibrinogenemia, Hypofibrinogenemia, Dysfibrinogenemia and Hypodysfibrinogenemia). The study of these mutations provides information not only for the patient, but also regarding the functional domains of fibrinogen. Additionally, high fibrinogen concentrations are a risk factor for cardiovascular diseases. Since fibrinogen levels are mediated by gene regulation, the fundamental study of fibrinogen gene regulation can help explaining the role of fibrinogen in cardiovascular diseases. During my thesis, I addressed both aspects of fibrinogen research by characterizing a new mutation leading to hypodysfibrinogenemia and by analyzing mechanisms that influence fibrinogen gene expression.