Wind direction measurements from a variety of indicators, taken over several Mars years and covering the entire planety, have been collected. These include observations of lee wave clouds not previously studied. The data exhibit a high degree of consistency and seasonal reproducibility, making it possible to interpret most of the observations in terms of the zonally symmetric circulation of Mars. We examine these data in the context of the constraints the observed wind directions place upon the thermal and polar cap mass flux fields which force the flows. Within the limitations of the data set, mid-, and high-latitude winds appear to be controlled by the thermal field during mid and late summer and winter, and in the northern hemisphere, during early sping and early summer. At other times, the cap flows dominate. At high altitudes, the strongest yearly winds are probably generated by cap formation in the north and cap recession in the south. The Hemispheric asymmetry seems to result primarily from the effects of global dust storms on the north polar cap. Turning of the prograde from poleward to equatorward in midautumn is observed, consistent with reduced poleward mass fluz and increased, meridional temperature gradient at that time. The latitudinal extent of the equatorial Hadley cell, when observed, is probably larger than that predicted by nearly inviscid models of low-latitude circulation. The cross-equational Hadley cell, and high-latitude poleward flows which occur in both hemispheres during the summer seasons, may set additional constraints on the therml forcing mechanisms at these times.