A product has been developed and tested, it goes to market. There it may pass through a product life cycle of four stages: introduction, growth, maturity, and decline. This cycle is a theoretical model of what happens to sales and profits for a product class over time. However, not all individual products follow the life cycle, and particular brands may act differently. Nonetheless, the product life cycle may provide some basis for anticipating future market developments and for planning marketing strategies. Different stages in the product life cycle call for different marketing strategies.