Lightner Witmer was one of the American students who took his doctoral degree under Wilhelm Wundt at Leipzig, and also one of the charter member of American Psychological Association. In 1896, he inaugurated the first psychological clinic at University of Pennsylvania. As a experimental psychologist, he played a number of crucial role in establishing and defining the clinical psychology as a helping profession. Clearly he was one of the great contributors in the development of psychology, yet he remains a shadowy, little known figure. This article summaries his life, carrier, and work without criticism.