Robert G. Cooper
A Stage-Gate ® system is a conceptual and operational map for moving a new-product project from idea though to launch and beyond—a blueprint for managing the product innovation process to improve effectiveness and efficiency.,  According to studies done by the Product Development and Management Association (PDMA) and the American Productivity and Quality Center (APQC), approximately 75% of U.S. product developers now use some form of Stage-Gate as the model to drive new-product projects to market., 
Stage-Gate breaks the product innovation process into a predetermined set of stages preceded by gates, as in Figure 24.1. Typically there are four, five, or six stages depending on the company and nature of the project. Each stage is comprised of a set of prescribed best practice activities designed to progress the project and to gather the essential information needed to make the next "go/kill" or investment decision. Following each stage, there is a go/kill decision point called a "gate", which is staffed by the senior management team, the owners of the resources required to move into the next stage. This incremental investment, stage-and-gate format led to the name "Stage-Gate system".
New products have an alarming failure rate. Of every nine new-product concepts, only one becomes a commercial ...