In preparing the present report, which covers the period July 1, 1984, to June 30, 1987, close collaboration has taken place between Commission 10 and 12, the two solar commissions, in order to avoid duplications and to insure that pertinent subjects are treated. The reader is referred to the report of Commission 12 for further solar topics. The proceedings are found at the beginning of the references for each section, followed by the usual alphabetical listing. In some sections this listing refers to the previous proceedings by their numbers; in others we retain the conventional reference. It is a pleasure to acknowledge the excellent work of the reviewers who wrote the different sections of this report, and all the members of the commission who provided information on research to be included.