Ecological Network Analysis (ENA) is a set of algorithms to evaluate the flow of energy and material through natural ecosystems from which a suite of systems properties can be derived. Ecosystem Network Analysis is used to investigate ecosystem structure and function, and is one component of the broader field of network ecology. ENA can be applied to characterize food web organization, assess ecosystem status and health, provide insight into the magnitude and structure of biogeochemical cycling of energy and material in ecosystems, and characterize the sustainability of urban metabolisms and other socio-ecological systems. ENA responds to the need for ecosystem-based management (of fisheries for example) and to characterize whole ecosystem structure, function and properties. Dynamic system properties can be derived from the ENA protocols that relate to the stability and resilience of ecosystems and the efficiency of energy utilization in ecosystems, aspects that have implications for sustainability and thus relevance to environmental and natural resource managers. Quantitative ecosystem flow networks of energy and material are being used in estuarine and marine environments to serve, for example, ecosystem-based fisheries and environmental management, and to assess the indirect impacts of fishing and pollution on the dynamics of exploited fish stocks and other living marine resources. ENA include a number of software programs that can be used for analytical, predictive and balancing of ecosystem flow models.