Studies of open innovation are predominantly concerned with firm-level strategy development. The result is that the literature has largely ignored the multiple contingencies that influence the implementation of an open strategy at the level of the NPD project. In this paper, we develop a conceptual framework of inbound open innovation at the NPD project level to assess factors that help determine the degree of openness along three dimensions. We argue that the margin of managerial action is not only constrained to the decision to open up the NPD project to a wide range of different types of external parties (breadth dimension), but that it is equally important to consider the depth of the relationships with different types of external parties (depth dimension) and the balance between the development of new and longstanding relationships (ambidexterity dimension). The calibration of these three dimensions represents the levers when managing an inbound open innovation strategy during an NPD project. Finally, we identify a range of contingencies, which potentially have a bearing on the appropriate calibration of the breadth, depth and ambidexterity dimensions of an open innovation strategy. We argue that appropriate calibration of the three dimensions of inbound open innovation is determined by the type of innovation (radical versus incremental), product complexity (discrete versus complex) and the appropriability regime (tight versus weak).