Effective cross-functional working relationships (CFRs) between Marketing Managers and R&D Managers are a key factor in successful new product development (NPD). Empirical evidence suggests however, that this CFR is often problematic. This article adds to our knowledge about Marketing/R&D CFRs during NPD by examining the effects of three forms of communication (communication frequency, bidirectionality, and quality) on two forms of conflict (dysfunctional and functional conflict). A hypothesised model of Marketing/R&D CFRs is tested using a sample of 184 NPD projects conducted in Australia, using R&D Managers as key respondents reporting on their relationships with the relevant Marketing Manager. Our findings reveal that communication quality and bidirectional communication, have strong effects on both forms of conflict. Also, the managerial use of frequent communication is ineffective in reducing dysfunctional conflict during NPD projects.