Party cohesion is crucial in parliamentary proceedings, for the strength of parties is determined by it. However high levels of party unanimity, parliamentary party cohesion is under no circumstances to be taken for granted. It is the outcome of a persistent struggle. From a rational choice point of view, the monitoring and sanctioning of recalcitrant MPs by the parliamentary party leadership is the condition sine qua non for party cohesion. Yet, rewards and punishments do not seem the cement that holds parliamentary parties together. Preliminary findings for the Belgian Chamber of Representatives, show that ministerial appointment, committee transfers, nor party list compilation are used systematicallyto this purpose.