The evolution of co-operative federalism is studied, with particular reference to the Spanish experience. Different types of relations between the centre and local government are described, the main models, instruments and mechanisms of collaboration between state and autonomous comunities - including sector conferences and conventions - are discussed. The involvemente of the decentralised bodies in the central state general policy is shown by the acceptance of the principles of co-operative federalism. According to ti, every significant government activity can be conducted by means of a jont and co-ordinate underatking by the central and member states. In Spain, the basis of relations between the state and autonomous communities is the principle of co-operationthat ensures the ordely performance of a state based on inter-action of the parties to it. The main models of collaboration between the state and the autonomous communities include co-ordination, co-operation and the duty of reciprocal aid. The constitutional justice body stresses the existence of a co-ordination power implicit in te sate that can be exerted in unilateral and compulsory manner. Instead, co-operation represents joint powers both of the state and the autonomous communities in the same are with shared responsibilities. The common duty to aid forces both parties to implement those activities needed for each of them, to exert in a tru and effective way it's own powers. Collaboration mechanisms among different territorial powers are needed, since the jurisdiction of institutions at different levels involve separate areas. Collaboration instruments may be multilateral or by sector - the state holds relations with all autonomous communities at the same time on specific topic - or bilateral - the state holds relations with each autonomous community. Sector conferences are meeting points between the central government and representatives of autonomous governments in order to exchange views, discuss problems and provide the means to solve them. Conventions are based on a different insight. While sector conferences are multilateral organisations with the participation of all communities based on the principle of equality, conventions cover the bilateral principle. Therefore, each autonomous community deals directly with the central state without trying to seek a common position with its counterparts. The Spanish system trend to take precedence over bilateral relations may reinforce system differences, since stronger communities can achieve better results