Innovation occurs only when an idea is put into practice. At the same time, R&D teams today experience increased time pressure, and creative ideas are likely to generate reluctance about their implementation. Consequently, there is a risk that novel ideas in projects do not receive the attention they need to mature enough to be selected for implementation. The aim of this paper is to expand our understanding of how idea maturity relates to idea selection in projects. To empirically explore this topic, data from five different R&D project teams engaged in idea development activities were collected via semi-structured interviews. Results indicate that idea maturity is situated at the interface between idea refinement and idea screening, as the construct incorporates both the refinement of the idea and contextual issues. Idea maturity is also shown to be a relative measure in that it is assessed by comparison to other ideas or existing products. Further, the frame of the project influences the maturity of ideas under development. For example, a shift in requirements for a project can reduce the maturity of an idea, highlighting a dynamic component in idea development.