William Esco Moerner (born June 24, 1953) is an American physical chemist and chemical physicist with current work in the biophysics and imaging of single molecules. He is credited with achieving the first optical detection and spectroscopy of a single molecule in condensed phases, along with his postdoc, Lothar Kador.Optical study of single molecules has subsequently become a widely used single-molecule experiment in chemistry, physics and biology.In 2014 he was awarded the Nobel Prize in Chemistry.

Moerner attended Washington University in St. Louis for undergraduate studies as an Alexander S. Langsdorf Engineering Fellow, and obtained three degrees: a B.S. in physics with Final Honors, a B.S. in electrical engineering with Final Honors, and an A.B. in mathematics summa cum laude in 1975.This was followed by graduate study, partially supported by a National Science Foundation Graduate Fellowship, at Cornell University in the group of Albert J. Sievers III. Here he received an M.S. degree and a Ph.D. degree in physics in 1978 and 1982, respectively. His doctoral thesis was on vibrational relaxation dynamics of an IR-laser-excited molecular impurity mode in alkali halide lattices.Throughout his school years, Moerner was a straight A student from 1963 to 1982, and won both the Dean's Award for Unusually Exceptional Academic Achievement as well as the Ethan A. H. Shepley Award for Outstanding Achievement when he graduated from college.

Moerner worked at the IBM Almaden Research Center in San Jose, California, as a Research Staff Member from 1981 to 1988, a Manager from 1988 to 1989, and Project Leader from 1989 to 1995. After an appointment as Visiting Guest Professor of Physical Chemistry at ETH Zurich (1993–1994), he assumed the Distinguished Chair in Physical Chemistry in the Department of Chemistry and Biochemistry at the University of California, San Diego, from 1995 to 1998. In 1997 he was named the Robert Burns Woodward Visiting Professor at Harvard University. His research group moved to Stanford University in 1998 where he became Professor of Chemistry (1998), Harry S. Mosher Professor (2003), and Professor, by courtesy, of Applied Physics (2005).Moerner was appointed Department Chair for Chemistry from 2011 to 2014.His current areas of research and interest include: single-molecule spectroscopy and super-resolution microscopy, physical chemistry, chemical physics, biophysics, nanoparticle trapping, nanophotonics, photorefractive polymers, and spectral hole-burningAs of May 2014, Moerner was listed as a faculty advisor in 26 theses written by Stanford graduate students.As of May 16, 2014, there are 386 publications listed in Moerner's full CV.