With this second volume of Advances in Catalysis, the editors have continued their efforts to present the many facets of the catalytic process. A number of highly qualified men have contributed to this volume. From the theoretical treatments of elementary processes between molecules reacting at solid surfaces to the technically important actions of fluoride catalysts, and to catalytic polymerizations of olefins, the reader will become acquainted with manifold ideas and with some typical experimental results relating to catalytic phenomena. Our lack of a complete understanding of catalytic action, and our corresponding inability to "predict" the best way of achieving a desired catalytic reaction, make it indispensable for everyone working in this direction to familiarize himself with the experience of others, even if such experience was gathered in remote sectors of this vast field.