Lai-Sang Lily Young (born 1952) is a mathematician from Hong Kong, who holds the Henry & Lucy Moses Professorship of Science and is a professor of mathematics and neural science at the Courant Institute of Mathematical Sciences of New York University. Her research interests include dynamical systems, ergodic theory, chaos theory, probability theory, statistical mechanics, and neuroscience. She is particularly known for introducing the method of Markov returns in 1998, which she used to prove exponential correlation delay in Sinai billiards and other hyperbolic dynamical systems.
Although born and raised in Hong Kong, Young came to the US for her education, earning a bachelor's degree from the University of Wisconsin–Madison in 1973. She moved to the University of California, Berkeley for her graduate studies, earning a master's degree in 1976 and completing her doctorate in 1978, under the supervision of Rufus Bowen. She taught at Northwestern University from 1979 to 1980, Michigan State University from 1980 to 1986, the University of Arizona from 1987 to 1990, and the University of California, Los Angeles from 1991 to 1999. She has been the Moses Professor at NYU since 1999.
Young became a Sloan Fellow in 1985, and a Guggenheim Fellow in 1997.