The present paper is part of a larger project by the same author that deals with the relationship between economic ideas and institutional change in post-socialist Russia. The paper develops two main theses: First, it argues that the concept of “developed socialism” as introduced by Leonid Brezhnev in 1971 on the one hand deprived the planned economy of political “mobilizing energy”, yet at the other hand prevented it from turning it into a self-organizing system. Thus it was, I argue, the perfect recipe for stagnation. Secondly, based on Imre Lakatos’ theory of scientific research programs, I argue that the concept of developed socialism in its official Soviet version can be seen as an attempt to cushion the critique of central planning that had developed in some of the Central Eastern European countries in the 1960s: By allowing some more, yet insignificant critiques (broadening the protective belt), the hard core of the ideological program (e.g. the structure of property rights) was made safer against criticism. The inability of Gorbachev’s economic advisors to provide practical guidance for reforms was, I argue, partly due to the fact that the ideology of developed socialism had favored an “idealist turn” in economics. As a result of this turn, the shestidesyatniki generation of Soviet political economists had rather little to say about economic reality.