Paper presented at the NATO Advanced Research Workshop ARW-STP 97464 on Reform of Government Scientific Laboratories developed at the University of Manchester, 3-5 June 1999. To be published in Philip Gummett, ed., Reform of Government Scientific Research Laboratories, Amsterdam: IOS Press, 2000 (in press).For almost thirty years the Spanish infrastructure for research and technological development was dominated by a single type of actor: Public Research Centres. All State efforts in R&D were channelled through PRCs, dependent upon specific Ministries. However in the eighties and in the nineties, Spanish Public Research Centres faced changes in their environment that simultaneously pressed them to make choices and offered them the instruments to adapt. The transformation of the environment in which PRCs operated was a consequence of both conscious political design aiming to reorganise the State action in support of research (the emergence of strategic R&D programmes) and of changes in the economic context of public research activity. A basic building block and a symbolic milestone of this reforming strategies was the approval in 1986 of the Law for the Promotion and General Coordination of Scientific and Technical Research (Law 13/1986), popularly known as the Law of Science. The Law made the PRCs more flexible to cope with the changes, by opening the door for diversification their sources of funding and by slightly changing from direct budgetary to non direct-budgetary appropriations. But these changes also contributed to enhance PRCs autonomy of decision vis à vis their ministries of affiliation and the independence of individual researchers from the authority of the PRCs directors. All these transformations, together with the stagnation and later reduction in real terms of direct budget appropriations in the nineties, resulted in new pressures and incentives for PRCs to adapt. How did these changes affect the funding strategies of Spanish PRCs? If we were to take the funding strategies of the PRCs as the behavioural variable to be explained, the question is to what extent did this new environment produce the "adaptive reaction" of the PRCs. If we were to take the funding strategies of the PRCs as the behavioural variable to be explained, the question is to what extent did this new environment produce the "adaptive reaction" of the PRCs. The response of PRCs to this new environment varied considerably. One group of PRCs did in fact begin to diversify its sources of income, increasing the importance of non-budgetary sources over the total income of the organisation. Other PRCs, on the contrary, remained much the same, despite the new opportunities opened by the new regulations. What we try tentatively to explain in this paper is this variation in the degree of adaptation of the PRCs, measured by the proportion of external non direct ministerial budgetary appropriations in their total expenditures. We argue that the diverse dynamics of change of the various PRCs, in response to the new environment, could be explained mainly through the analysis of the institutional arrangements and organisational variables. We assume relevance of historical processes, that is "path dependency" and "organisational inertia". In other words, the diversity of outcomes observed when PCRs are confronted with similar changes in their environment is attributable to the different institutional arrangements and trajectories of each organisation. Our task here is to find commonalties and differences.Peer reviewed