Carlos Sonnenschein was trained as a Medical Doctor and qualified as a Doctor in Medicine at the School of Medicine, University of Buenos Aires (UBA), in Argentina. He practiced as a pediatric endocrinologist for 5 years. He then turned toward the sciences and trained as a cytogeneticist at the UBA Faculty of Sciences. In 1965, he migrated to the USA and settled at the Children’s Hospital in Boston. In 1969, Sonnenschein was appointed as Assistant Professor at Tufts University School of Medicine; in 1980 he became Full Professor there, a position that he occupies today. His research interests were primed by a three-month period spent in Paris, France, in 1970, at Hôpital Bicêtre (with Etienne-Emile Baulieu, INSERM) where he engaged in studying the control of cell proliferation by estrogens. Back at Tufts University, he built an experimental laboratory group dedicated to study the above referred subject. In the late 1980s, in collaboration with Professor Ana Soto, they serendipitously discovered that synthetic estrogens were shed from plastic centrifuge tubes. As a result, together, they established the bases of the field of environmental estrogen disruptors (EED). In 1999, they published a book, The Society of Cells, in which they proposed the tissue organization field theory of carcinogenesis (TOFT). Sonnenschein has been active in this research field in which he combines cancer research and developmental biology.