The many seminal contributions made by Professor Nam P. Suh to the theories of wear, such as the delamination wear and the solution wear, are well known. The contributions made by him and his associates to the theories of friction, however, are less known; but they are equally significant. In this article, I first briefly survey, to provide an historical context, the laws and theories of sliding friction as proposed over the past centuries and decades. Then the contributions of Prof. Suh and his associates in recent decades are reviewed. Specifically, the role of wear particles in the frictional phenomena...