The existing nomenclature for Martian surface features is a rich profusion of allusions to classical literature—and not in all cases familiar to the modern planetary scientist. With the forthcoming space vehicle exploration of Mars, problems of Martian nomenclature will begin to increase in importance. Icarus is fortunate to be able to publish this explanation of the currently accepted Martian nomenclature by T. L. MacDonald, F.R.A.S., who was Director of the Lunar Section of the BAA at the same time that E.-M. Antoniadi was Director of the Mars Section. The manuscript has been kindly provided and edited by Dr. R. A. Wells, Space Sciences Laboratory, University of California, Berkeley, California 94720. Dr. Wells has also provided the accompanying map, which he stresses is intended to be schematic only. Not all the features mentioned by MacDonald are currently accepted IAU nomenclature. The naming of linear features on this map is not intended as a commitment to their reality—only as a guide to understanding the classical literature of Mars. Dr. Wells points out that in reading the following text, italicized names in general refer to regions on Mars unless obviously the title of a book. Initially capitalized names in Roman print are the sources for the italicized versions unless simultaneous reference is made both to the Martian name and its source.