Ecological Network Analysis (ENA), based on network theory, is a methodology to quantify how objects interact with and depend on other objects in a system. Primary results from the method provide structural and functional properties of networks. A subset of ENA, Network Environ Analysis, divides the network into input and output “environs.” Application on empirical datasets and ecosystem models has revealed several important and unexpected results that have been identified and summarized in the literature. Data requirements for the analysis include the intercompartmental flows, compartmental storages, and boundary input and output flows. This article reviews the theoretical underpinning of several types of analyses of networks and briefly introduces some the main properties such as indirect effects ratio, network homogenization, network mutualism, ascendency and robustness. References for further reading are provided.