The basic differences between marketing managers and their technically trained counterpart managers [e.g., research and development (R&D), engineering, and manufacturing managers] in terms of work experience, training, and differing decision-making styles have often been suggested as a source of conflict, which acts as a barrier to effective working relationships and integration during new product development (NPD) work. In this paper, we empirically explore this issue by developing and testing a model of psychosocial differences (thought worlds and psychological distance) between the two groups of managers and their effect on communication, trust, and relationship effectiveness during NPD projects. We find that while thought world differences do still matter, it was from a marketing perspective that they had a stronger effect. These findings have implications for top management trying to manage the functional manager interface during NPD projects. We propose a semi-formalized approach to relationship building that may speed up the acquisition of social data that is often necessary to elevate working relationships to trusting ones and improve the efficiency of NPD work. Our model is tested using data from two samples, 184 technically trained managers and 145 marketing managers from Australian companies involved in NPD work.