This volume contains review articles which were written by the invited speak ers of the Sixth International Summer Institute in Surface Science (ISISS), held at the University of Wisconsin-Milwaukee in August 1983. The objective of ISISS is to bring together a group of internationally recognized experts on various aspects of surface science to present tutorial review lectures over a period of one week. Each speaker is asked, in addi tion, to write a review paper on his lecture topic. The collected articles from previous Institutes have been published under the following titles: Surface Science: Recent Progress and Perspectives, Crit. Rev. Solid State Sci. 4, 124-559 (1974). Chemistry and Physics of Solid Surfaces, Vol. I (1976), Vol. II (1979), Vol. III (1982) (CRC Press, Boca Raton, FL), and Vol. IV (1982), Springer Ser. Chern. Phys., Vol. 20 (Springer-Verlag Berlin, Heidelberg, New York 1982) No single collection of reviews (or one-week conference for that matter) can possibly cover the entire field of modern surface science, from heter ogeneous catalysis through semiconductor surface physics to metallurgy. It is intended, however, that the series Chemistry and Physics ofSolid Sur faces as a whole should provide experts and students alike with a comprehen ve set of reviews and literature references on as many aspects of the subject as possible, particular emphasis being placed on the gas-solid interface. Each volume is introduced with a historical review of the devel opment of one aspect of surface science by a distinguished participant in that development."

At the International Summer Institute in Surface Science (ISISS), which is held bienially on the Campus of the University of Wisconsin-Milwaukee, invited speakers present tutorial review lectures during the course of one week. The majority of the presentations deal with the gas-solid interface, but now and then relevant reviews concerning liquid-solid or solid-solid interfaces are included. The goal of ISISS was outlined in the first ISISS publication: "We recognize that the International Summer Institute in Surface Science should foster mutual understanding and interaction among theorists and experimentalists in the various areas of surface science. Progress can be achieved only when we occasionally peek over the fence into neighboring areas, not so much to amuse ourselves that the grass is greener on the other side as to learn from their progress and, perhaps equally fruitfully, from their limitations and setbacks. In addition, it is an important task in any field of science to assess, take count of what is done and, what is more important, to point in future directions. " Since the foundation of ISISS in 1973, the invited speakers - internation ally recognized experts in their area of specialization - have been asked to write review articles too. We wanted in this way to ensure that the largest possible group of scientists could benefit from the special review concept."