The normal stages that a product passes through: research and development, growth, expansion, maturity, saturation, and decline. In the research stage, there are no sales at all. In the growth stage, sales are slow and often need to be supplemented by heavy sales and advertising efforts. In the expansion stage, sales may grow more rapidly. In the maturity stage, sales start slowing down as most people who might want the product already have it. In the saturation stage, everyone who wants the product has it, and there are few opportunities for increasing sales. In the decline stage, sales fall and the product eventually becomes obsolete.