In this article we report on the design, prototyping and results of a research effort aimed at identifying whether and how trust affects the innovativeness of a partnership between two players. The methodology combined an experiment and two questionnaires. The research aimed to increase our understanding of trust and its impact on the innovative outcome of cooperation and to derive some guidance for economic actors, namely R&D managers and executives who intend to build innovation-oriented relationships with their business partners. Specifically, we investigated the effect of trust on partners' creativity and willingness to invest financially in a joint development. Our results show that more trustful partners invest higher amounts in the alliance, while there seems to be an optimum amount of mutual trust between partners who maximize their joint creativity and innovativeness; if the level of mutual trust is below or above this threshold, their joint creativity seems to increase less or even to decrease. Our findings suggest that joint development projects should always include explicit trust development activities at the beginning of the project, and that the amount of trust in the joint team should be monitored to avoid the negative consequences of excessive trust.