This article contributes to the network effectiveness literature by identifying the theoretical mechanisms and network measures scholars in public administration and policy use to draw inferences between network structures and network effects. We conducted a systematic review of empirical network effects research in 40 journals of public administration and policy from 1998 to 2019. We reviewed and coded 89 articles and described the main social theories used in the network effectiveness literature and the associated mechanisms that translate network structures to network effects. We also explain how scholars operationalize those theoretical mechanisms through network measures. Overall, our findings reflect that there is a limited use of social theories for the explanation of network effects and in some cases, there is an inconsistent use of network measures associated with theories. Moreover, we identify the main challenges related to network effects, including the difficulty of isolating specific mechanisms related to a particular social theory, the use of network structures both as a mechanism and as a measure, and the lack of data to examine network dynamics and coevolution.