The ground-based research activity in the planetary field has increased very rapidly since the Prague meeting in 1967. The space probes into the atmosphere of Venus and the flybys of Mars have not only added directly to our knowledge of these planets but have stimulated further research.

Because of this rapid growth and the large expense which would be required to publish detailed descriptions of the very numerous research projects carried on in the last three years, this report will differ in important respects from the previous ones. Drs Levin, Pettengill, and McElroy have provided summaries of progress made in three important fields of planetary science, and Levin has also kindly contributed a summary of planetary research carried on in the U.S.S.R. since the Prague meeting. On behalf of its members, the President of Commission 16 gratefully acknowledges each of these important contributions.