Michael E. Porter is a Harvard Business School professor and a leading authority on competition and strategy. This book is a landmark in the field of strategy/strategic management, and Porter's view has later become known as the positioning school. The book provides a great framework.
The book consists of three parts - General Analytical Techniques, Generic Industry Environments, and Strategic Decisions. In addition, the two appendices - Portfolio Techniques in Competitor Analysis, and How to Conduct an Industry Analysis - should also be mentioned as they are very useful.
In Part I, Porter discussess the structural analysis of industries (with the world-famous five forces), the three generic competitive strategies (overall cost leadership, focus, and differentiation), an excellent framework for competitor analysis, competitive moves, strategy toward buyers and suppliers, structural analysis within industries (strategic groups, strategic mapping, mobility barriers), and industry evolution (life cycle, evolutionary processes).
In Part II, Porter discusses competitive strategy within various generic industry environments, such as fragmented industries (with no real market leader), emerging industries (e-commerce and Internet are excellent examples, although not mentioned in this book as it was written in 1980), mature industries, declining industries, and global industries.
In Part III, Porter discusses strategic decisions which businesses/firms can take, such as vertical integration (forward, backward, partnerships), capacity expansion, and entry into new industries/businesses.
Even after 20 years, most of this book still stands strong, although some people will argue this. It is a MUST for MBA-students and all other people interested in strategy/strategic management. The book is good to read (simple US-English) and thus does not become a struggle.