Este trabajo es uno de los frutos de las actividades preparatorias del proyecto de investigación “Reformas en el Estado de Bienestar: actores y apoyos ciudadanos (REBAAC), http://www.iesam.csic.es/proyecto/rebaac-en.htm, dirigido por el profesor Luis Moreno. Una versión anterior fue presentada en Barcelona (España) durante Congreso Nacional de Ciencia Política en septiembre de 2003 y se ha beneficiado de los comentarios realizados por los integrantes del taller de Políticas Sociales Comparadas, en especial, de Elisa Chuliá. También agradezco sus valiosos comentarios a Luis Moreno y a César Colino.From the 1970s on there has been continuous discussion about the Welfare States crisis, followed in the next decade by a concern with welfare reform. Some very significant and influential studies and research argued that the force of some immovable objects had provoked that welfare state reform was only incremental, limited to adjustment of some welfare institutions or programmes. New empirical evidence, however, has established the occurrence of deeper reforms in welfare going beyond incremental changes. In this article I discuss the concept of reform and its scope. Additionally, I try to analyse what are the facilitating conditions and what strategies have been utilized by reformist governments to guarantee success and avoid the resistance to change of public opinion, the interest group, the institutions and the existing welfare policies.