The theory of almost periodic functions is a well established branch of modern mathematics, with roots in the work of mathematicians as H. Poincare, P. Bohl and E. Esclangon. The essentials of the theory have been published by H. Bohr (1922{1926), whose work immediately attracted the interest of many distinguished mathematicians like V. Stepanov, S. Bochner, H. Weyl, N. Wiener, A.S. Besicovitch, J. von Neumann, N.N. Bogolinbov, with significant contributions to the field.