THE TRADITIONAL articulation ENTRY FINANCEMENT AND MANAGEMENT OF SOCIAL SECURITY SYSTEM IN BELGIUM: NECESSITY OR CONTINGENCY? A NEO-INSTITUTIONAL LECTURE: ‘Etatism is a bureaucracy that engages in isolation tending to omnipotence, but ultimately asleep in inertia. On the contrary, joint management is always alive because it is subject to the top management of direct representatives of the people themselves’ (Fuss, 1951). Social security comparators characterise the types of welfare state according to various criteria, including the methods of management (state or parity) and financing (based rather on tax or social security contributions). From this perspective, the interdependence of a social security system, the financing of which depends primarily on contributions to work and its management by the social partners — two principles underpinning the Belgian model introduced by the Social Pact in 1945 — is a characteristic feature of continental (or ‘conservative’ or ‘corporatist’) social security models. The involvement of the social partners in management, on the one hand, and financing based on contributions, on the other, is seen as a clear and necessary element, including by the social security stakeholders themselves. The Law of 18 April 2017 reforming the financing of social security seems to confirm this, now classic, hypothesis of the inseparability of the nature of the resources and the method of management of social security: after a long period of development, it devotes — without replacing it — the end of this financing and management model and its transformation into an ‘anglo-Saxon’ or ‘liberal’ welfare state, largely financed by the general state budget and managed by the executive. Its provisions could lead to a growing inability of social security to fulfil its tasks. Since 2010, the initiation of a process of defederalisation of social security has further aggravated the risks posed both to the guarantee of its financing and to the involvement of the social partners in its management. This article shows that the interdependence between management and financing, which is assumed to be necessary, must in fact be understood in the light of the dual matrix, well before the 1945 Pact, which saw it emerge: an economy based on industrialisation, and a form of government ‘in Belgium’ marked by consultation, which was present since the constitution of Belgium in 1830 and has been gradually eroded since the 1970s. That reading makes it possible to envisage as a contingent the link between the form of management and the nature of the financing and suggests that the social partners are involved in the management of social security irrespective of changes in the sources of its financing. Within the limits of this text, we focus on the evolution of the main features of the management and financing — particularly by the ONSS — of the scheme for employees, although we are well aware that certain sectors such as the health care sector have specific and exciting features. Their more in-depth analysis deserves to be carried out, from the same point of view, even though it seems to me unlikely that it invalidates our central assumptions. Our demonstration will follow the historical thread of the relationship between, on the one hand, management and financing principles and, on the other hand, the transformation of their original matrix. A first part will show how this model has anchored and consolidated in an economic and institutional matrix that has been developed and strengthened until the 1970s. The second part will present the erosion of the founding principles, in line with that of this double matrix, and their radical degradation over the last two legislatures.