Our approach in this survey, treading in Hotelling's footsteps, has been to use location theory to formulate precisely some issues that economic theory can no longer neglect. Among them are the following: What is an industry? What are the price and quantity outcomes in industries where conscious interaction among firms is explicitly recognized? How does nonprice competition operate among firms acting under price agreements? How does entry lead to an endogenous determination of industry size and firms' profits?