Porter's Five Forces is a model of industry competition. It is a tool used to analyze the competitive environment in terms of five key forces that affect a company's profitability and influence its strategy.
Michael Porter set out the Five Forces model in two articles published in the Harvard Business Review.
"The Five Competitive Forces That Shape Strategy." Harvard Business Review 86:1 (January 2008): 78-93.
"How Competitive Forces Shape Strategy." Harvard Business Review 57:2 (March/April 1979):137-145.
Articles from the Harvard Business Review are online in the database Business Source Complete.