Dr. Lightfoot writes mainly on syntactic theory, language acquisition and historical change, which he views as intimately related. He argues that internal language change is contingent and fluky, takes place in a sequence of bursts, and is best viewed as the cumulative effect of changes in individual grammars, where a grammar is a "language organ" represented in a person's mind/brain and embodying his/her language faculty. That, in turn, entails a non-standard view of language acquisition as "cue-based." He has published eleven books, most recently The Development of Language (Blackwell, 1999), Syntactic Effects of Morphological Change (ed.) (Oxford UP, 2002), The Language Organ (with S.R. Anderson) (Cambridge UP, 2002), and How New Languages Emerge (Cambridge UP, 2006). He is also the author of more than 100 articles, book chapters and reviews. He is general editor for the Generative Syntax series published by Blackwell, and serves on the linguistics editorial board at Cambridge University Press. In 2004, he was elected a fellow of the American Association for the Advancement of Science, and in 2006, as a fellow of the Linguistic Society of America. He has been elected as President of the Linguistic Society of America, serving 2010-2011.

Dr. Lightfoot has held regular professorial appointments at several universities including McGill University, where he taught many undergraduates who went on to become major figures in linguistics and psychology including Mark Baltin, Alan Prince, Michael Rochemont, Alison Gopnik, Elan Dresher, Norbert Hornstein, Amy Weinberg, Renée Baillargeon and Elizabeth Cowper; the University of Utrecht in the Netherlands; and the University of Maryland, where he established and chaired for 12 years, a new department of linguistics with a unique focus--viewing linguistics as the study of the human language organ. He was also the associate director of the neuroscience and cognitive sciences program there. In 2001, he moved to Georgetown University as dean of the graduate school. From 2005 to 2009 he served as Assistant Director of the National Science Foundation, heading the Directorate for Social, Behavioral and Economic Sciences. In 2009 he returned to Georgetown, where he is directing the undergraduate interdisciplinary program in cognitive science and the graduate program in Communication, Culture & Technology. In addition, he has held short-term appointments at universities in Austria, Brazil, Canada, Germany, Switzerland and the United Kingdom.

His honors include a Fulbright Scholarship, a Ford Foundation Fellowship, an American Council of Learned Societies Fellowship, three National Science Foundation research grants, various research grants from the University of Maryland, and a Fulbright Distinguished Chair position at the University of Trieste (2010).