The past decade has seen rapid proliferation of research that has revitalized the study of food webs and ecological networks. New techniques and applications have been published at a very rapid pace, with hundreds of publications in ecological journals addressing network properties. It is now crucial to focus this new knowledge and propose experimentally testable theories and practical tools that could be applied in the conservation of ecosystems and the restoration of damaged ecological networks. This symposium will focus on the assembly of ecological communities (restoration) and the collapse of ecological networks (conservation) from a perspective encompassing multiple trophic levels. In particular, this session will highlight and synthesize recent developments in food web theory and practice that target the identification of (1) key species that play a fundamental role in maintaining ecosystems’ functions and services, and (2) key properties in the structure of links between species that are critical to the overall robustness and resilience of ecosystems. We define ecological networks to encompass food webs as well as mutualistic and parasitic webs. Contributions from other fields will be included, with particular emphasis on translating network measures from sociology and physics into ecologically meaningful criteria that can lead to the assessment of ecosystems’ health. Speakers will synthesize current knowledge and propose new research.