This symposium was part of the Spring College on Fusion Energy. It consisted of about three dozen talks (some of which will be issued in an IAEA document in the ICTP Series). The agenda as given turned out to be broader than the title of the symposium indicates. I have grouped the contributions into five categories as given below, hoping that the papers selected here will reflect the flavour of those talks most directly related to the original topic of the symposium. The papers had no reference numbers and will be referred to by the names of their first authors.
