This publication is one in a series of volumes devoted to planetary positional and geometric data. The present Volume III provides information describing the planet Mars. Other volumes to be published in 1983 are II, IV, and V, describing Venus, Jupiter, and Saturn geometric data, respectively. The presentations of planetary positional and geometric data for Mercury (Volume I), Uranus (Volume VI), Neptune (Volume VII), and the Pluto/Charon System (Volume VIII) will be published later. This publication contains graphical data necessary for the analysis of planetary exploration missions to Mars. Positional and geometric information spanning the time period from 1990 through 2020 is presented; the text explains the data and its usage. This volume is one in a planned series covering planetary mission targets. The purpose of this series of planetary geometry handbooks is to provide mission and science planners, as well as trajectory designers with graphical information sufficient for preliminary mission design and evaluation. It is intended to be used in conjunction with the appropriate volumes and parts of the Mission Design Handbooks. It extends their coverage by commencing in 1985 and continuing to the year 2020. This time span was chosen to provide sufficient mission duration flexibility for all Earth departures through 2005. The present Volume III is devoted to data on the positions of the planet Mars. It presents information characterizing the geocentric and heliocentric positional geometry of a spacecraft while it is in the vicinity of the subject planetary body. The spacecraft could encompass a lander, an entry probe, or a flyby vehicle at encounter. Such wide usage of the data is possible because planetary positions change but slowly while the distances to Earth or Sun are always large compared to those between the spacecraft and the target planet during the encounter.