It is perhaps one of the most important characteristics of the past decade in astronomy that the evolution of some major classes of astronomical objects has become accessible to detailed research. The theory of the evolution of individual stars has developed into a substantial body of quantitative investigations. The evolution of galaxies, particularly of our own, has clearly become a subject for serious research. Even the history of the solar system, this close-by intriguing puzzle, may soon make the transition from being a subject of speculation to being a subject of detailed study in view of the fast flow of new data obtained with new techniques, including space-craft.

The present report deals with the basic facts of extra-galactic astronomy. It should be noted that a true picture of the outer stellar systems (galaxies) was formed in astronomy only about forty years ago. As a result, most basic problems concerning the outer galaxies remain unresolved. We, therefore, formulate in the present report a number of problems which, in our view, seem to constitute the most essential points in the further exploration of the outer galaxies. We shall try to keep as close to the facts as possible and handle, primarily, those problems the solution of which may seem possible in the near future with the means available to us.