Traditional Reformation scholarship argued that conceiving faith as a habit is one of the differences between Reformed orthodoxy on the one hand, and Reformation thought on the other. Two theses have been defended in this respect. First, it has been argued that conceptualising faith as a habit was a typical example of introducing Thomistic and Aristotelian concepts into the Reformed faith. Secondly, several scholars have argued that the conceptualisation of faith as a habit overrules the role of the act of faith in salvation. The function of faith as a response to God's offer of salvation becomes secondary to the doctrine of predestination. By unravelling the transformation process which the concept of habit underwent through the history of Christian theology, the author shows that the first thesis is seriously flawed. As to the second thesis, he proposes an alternative interpretation of the sources by arguing that the nature of faith as a habit implies that it can only be known from its acts. At the end of the article, he provides some remarks about the value of the concept of habitus fidei for contemporary theology.