The content of separation of powers is neither defined in constitutions, which usually do not explicitly guarantee this principle, nor in other legal texts. Its content cannot be circumscribed with precision. Several influential authors have dealt extensively with separation of powers. However, few of them were constitutional and economic thinkers. After careful analysis, but without claiming to be exhaustive, two major names stand out. The connection between reflections by Montesquieu and Hayek on the concentration of state power on one hand, and on economic concentration on the other hand, is illuminating and fascinating, but has never before been established. Aron also deserves a special mention in this regard, as he notably dealt with democracy and totalitarianism as well as competition in the same breath throughout some major parts of his work.