The social protection system in Castilla y León is characterized, as in the other regions of the Spanish State, by adopting a “welfare mix” model in which public and private agents collaborate with different roles and from different positions. This paper analyzes the role played by the Third Sector (voluntary sector) and its relationships with public administrations within the framework of social inclusion policies in Castilla y León. The way in which the public-private relationship takes place in this particular area of public management constitutes a differentiating fact that distinguishes the case of Castilla y León in relation to other Spanish regions.