In this paper we investigate the dynamics of networks of employees in the front end of the new product development process. So far, the literature has focused on network structure and has argued that sparse (low density) networks of weak ties are optimal for idea generation. In this paper we include both network structure and network content, and we emphasize the importance of strong ties, density, range, seniority and decision-maker involvement in specific phases of the front end in an environment of uncertainty, ambiguity and tacit knowledge. To test our assumptions, we mapped the full networks of 17 ideas for new product development projects over time in a longitudinal study in two research laboratories. For specific phases of the front end, we found confirmation of our expectations. In addition, it appeared that particularly strong ties between different units advance the adoption chances of ideas. The managerial implication of this latter finding is that communication with good acquaintances or friends in other units should be promoted in the front end of idea generation.