Michael Porter's 1980 book gave competitive analysis a formal structure and supplied the vocabulary the subject still uses.

Five forces

Porter argues that the profitability available in an industry is set by five structural forces: rivalry among existing firms, threat of new entrants, threat of substitutes, bargaining power of buyers, and bargaining power of suppliers.

The implication is uncomfortable. Most of the variation in returns is explained by which industry a firm is in rather than how well it is run. A capable firm in a structurally poor industry — fragmented, easy to enter, with powerful buyers and available substitutes — will earn less than a mediocre firm in a protected one. Strategy starts with an honest reading of the forces.

Generic strategies

Porter identifies three defensible positions. Cost leadership means being the lowest-cost producer and earning above-average returns at the prevailing price. Differentiation means being valued for something buyers will pay a premium for. Focus means applying either to a narrow segment.

His warning is against the middle. A firm that pursues cost leadership and differentiation at once tends to achieve neither, carrying the cost structure of a differentiated business and competing on price. He calls this stuck in the middle, and it remains the most common strategic failure in small firms.

Barriers and rivalry

The book is most detailed on entry barriers — economies of scale, switching costs, capital requirements, distribution access — and on what makes rivalry destructive. High fixed costs, undifferentiated products and slow growth produce price competition, which is why an industry can grow and be unprofitable at the same time.

Using it

The framework works as a diagnostic before committing resources. Applied to a service business, it usually explains why a founder is working hard for thin margins: low entry barriers, powerful buyers, and no differentiation that survives a price comparison. See positioning and client concentration.