This chapter analyzes an equilibrium model where privately owned firms feature either smooth decreasing or constant returns to scale. Profit of the constant returns to scale firms being equal to zero at equilibrium, the equilibrium of the model does not depend on the ownership structure of these firms. In addition, the convex conical production sets of these firms sum up into a convex cone. It is as if the production sector operating under constant returns consists of a unique firm. The general equilibrium model with decreasing and constant returns to scale firms is essentially the same model as the one considered in Chapter 10 with the addition of a unique firm operating under constant returns to scale. Nevertheless, this addition is enough to hamstring the approach of the preceding chapters based on the concept of price system that equates aggregate supply and demand. The solution is to add to that price system the activity of the constant returns to scale firm.