The first NATO Science Forum was held in Biarritz in September 1990. This Taormina Conference is the second in a series that we wish to be a long one and I believe that it has equalled the success of its predecessor. In setting up these meetings the NATO Science Committee wanted to gather leading experts to review fields of strong present interest. It was intended that presentations and discussions should pay special attention to potential developments. This "forward look" is indeed precious to us in mapping out the evolution of our Science Programme but more importantly, it is an essential...