The Linear Model of Innovation was an early model designed to understand the relationship of science and technology that begins with basic research that flows into applied research, development and diffusion 
It prioritizes scientific research as the basis of innovation, and plays down the role of later players in the innovation process.
Current models of innovation derive from approaches such as Actor-Network Theory, Social shaping of technology and social learning, provide a much richer picture of the way innovation works. Current ideas in Open Innovation and User innovation derive from these later ideas.
In the 'Phase Gate Model' , the product or services concept is frozen at an early stage to minimize risk. Through enterprise, the innovation process involves a series of sequential phases arranged in a manner that the preceding phase muse be cleared before movie to the next phase. Therefore a project must pass through a gate with the permission of the gatekeeper before moving to the next succeeding phase.
Criteria for passing through each gate is defined beforehand. The gatekeeper examines whether the stated objectives for the preceding phase have been properly met or not and whether desired development has taken place during the preceding phase or not.
Two versions of the linear model of innovation are often presented:
From the 1950s to the Mid-1960s, the industrial innovation process was generally perceived as a linear progression from scientific discovery, through technological development in firms, to the marketplace. The stages of the "Technology Push" model are:
From the Mid 1960s to the Early 1970s, emerges the second-generation Innovation model, referred to as the "market pull" model of innovation. According to this simple sequential model, the market was the source of new ideas for directing R&D, which had a reactive role in the process. The stages of the "market pull " model are:
The linear models of innovation supported numerous criticisms concerning the linearity of the models. These models ignore the many feedbacks and loops that occur between the different "stages" of the process. Shortcomings and failures that occur at various stages may lead to a reconsideration of earlier steps and this may result in an innovation. A history of the linear model of innovation may be found in Godin The Linear Model of Innovation: The Historical Construction of an Analytical Framework.