He is also an adjunct professor of law at the Washington College of Law of the American University. Professor Williamson is a principal in the Falls Church, Virginia accounting firm of LaMonaca & Williamson, CPAs which specialize in tax compliance and planning for small businesses and individuals. He is a frequent lecturer to professional groups and has published numerous articles. Previously, Professor Williamson was senior manager for international taxation at the National Tax Practice Office of KPMG Peat Marwick in Washington, D.C. He is a frequent lecturer to professional groups and has published numerous articles.