This article seeks to describe and understand relational interaction processes in project networks, and suggests that there is a connection between the characteristics of a project network and the type of interactions within it. We suggest that time, legitimacy and power structure determine the type of interaction processes that occur. Four case studies of service-producing project networks show that relational interaction processes tend to change over time-shifting between the dimensions of consent and negotiation. Project networks seeking to acquire legitimacy are characterised by consent-based interaction processes such as mapping by rhetoric and maintaining an element of vagueness. Legitimate project networks are, on the other hand, characterised by negotiation-based interaction processes such as meetings between the representatives of different interests. Thus, actors in different types of project network adopt different interaction strategies in managing project networks with a view to creating legitimacy or mutual commitment. (c) 2007 Elsevier Ltd. All rights reserved.