Abstract
Target space duality is a remarkable phenomenon where different 2-dimensional nonlinear sigma models are physically equivalent. A key reason for interest in this subject is that duality often turns a strong coupling problem into an equivalent weak coupling one thus transforming an intractable problem into a manageable one. There are two questions which immediately come to mind. The difficult one is: given a sigma model does there exist a dual model? A more accessible one is: when are two sigma models dual to each other? In these lectures we will attempt to address the latter question within the framework of classical hamiltonian mechanics.