There is a growing body of literature on the importance of proximity for innovation and other knowledge-related outcomes. We examine the impact of geographical, social, organisational, and cognitive proximity for a heterogeneous population, including people from academia, knowledge institutes, industry, and government. We analyse data on 1020 ego-alter relationships, derived from a survey among water professionals in the Netherlands. The use of survey data allows for more refined indicators of

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... roximity and more diverse collaboration outcomes than those common in the literature. Social and cognitive proximity have a positive effect for all outcomes examined. Geographical and organisational proximity have a negative effect on hard (tangible) outcomes yet a weak positive (if any) effect on soft (intangible) outcomes. We do not find evidence for the suggestions in the conceptual literature that proximity follows an inverted U-curve where most outcomes are achieved in relations with some but not too much proximity.