First, he probed deeply into one specific aspect of their model-the assessment of the external environment, in particular the competitive situation the firm faces in its industry. In his highly successful 1980 book Competitive Strategy, Porter developed rather specific and detailed procedures for analyzing both competitors and industry structures in general. A summary of these ( from a Harvard Business Review article) is presented in this chapter. Second. Porter also focused attention on a specific triad of generic strategies. He suggests-as can be seen in the second excerpt, from his 1985 book Competitive Advantage-that all competitive strategies can be reduced to three basic ones : (1) cost leadership, (2) differentiation, and (3) focus. Third, Porter developed several interesting views of how strategies tend to cluster : by type of industry, by groups within an industry, and so on. We present some of these basic ideas from Porter's writing in this chapter; some of his other concepts, on generic industry situations, appear in the "Contexts" section of the text.