Although for a long-time symbiosis was considered to be quite rare and with no role in evolutionary processes, Lynn Margulis demonstrated that endosymbiotic events played a key role in the origin and evolution of eukaryotic cells. Starting with her seminal assay in the Journal of Theoretical Biology in 1967 (authored as Lynn Sagan), her lifelong work on eukaryogenesis and the role of symbiosis in evolution stands as a valid and authoritative contribution to science. As was quick to acknowledge, she was not the first to discuss the significance of symbiosis to explain the origin of mitochondria and chloroplasts, but no one else had done it to her extent and depth, nor had anyone provided a variety of testable hypotheses. While it is true that some of her proposals were incomplete or mistaken, morphological, biochemical and geochemical evidence together with phylogenomic analyses of mitochondria, chloroplasts and eukaryotic nuclear genomes have demonstrated the validity of her evolutionary scheme, as well that of her specific predictions on the chimeric nature of genomes and the mosaicism of metabolic pathways in eukaryotic cells. (C) 2017 Elsevier Ltd. All rights reserved.