The focus of this paper is to share thinking about networks in action research (AR) and to consider their role, purpose, and how networks' outcomes and impacts might be evaluated. Networks are often a by-product of AR projects, yet research focused on the network itself as part of a project is rare. The paper is one of several associated with the Evaluative Study of Action Research (ESAR) in which we wish to understand how projected outcomes and impacts are realised and why certain approaches are chosen and seen to be effective. Description is provided of the development and function of networks and their connection to, and within, AR. We then explore the first of a series of networks in the ESAR, the core team network, and undertake a formative evaluation of the functioning of this network. The paper concludes with a look ahead to the evaluation of each of the various levels of networks anticipated within the ESAR.