The Belgian constitutional system is based upon the classic principle of the trias politica, which means that there is a separation of powers, but also a balanced cooperation between them. This article focuses on the Belgian federal Parliament, which bas been, together with the reform of the state from a unitary to a federal state, radically reformed. The Belgian Parliament nowadays is much better equipped to fulfil the function of checks and balances than thirty years ago. The number of staff and the material equipment has increased considerably. At the same time, the emphasis in parliamentary activity bas shifted from the plenary session to the committees. The control upon the budget was long time a nearly empty box. Since the reform of 1989, it has become a much stronger instrument to hold the government to account. The annual debate on the budget is rather a genera/political evaluation of the government policy and is always ended by a vote of confidence. As for the law-making function, the share of the government in adopted laws is much higher than that of Parliament. Parliament bas still the power to amend government bills, but this power is limited because there is often already an agreement between the government and the parliamentary party of the coalition-parties. Nevertheless, several important amendments have been adopted in the last legislature. The control function bas evolved in different directions. Due to an enormous increase in the number of interpellations, they have lost a great part of their importance. They constitute no langer a real threaten to the survival of the government. On the other hand, there are more oral and written questions than before and the use of parliamentary inquiry committees has augmented considerably. Despite their inherent shortages, these committees play, an important role in preparing and correcting policy. The new challenges for Parliament in the future are serving as forum of the nation and the evaluation of laws. The core business of the trias politica, namely budgetary, law-making and controlling duties, also remain to befulfilled by Parliament.