Mars Orbiter Laser Altimeter (MOLA) data have been used to construct Digital Elevation Models (DEM) of the Martian volcanoes in order to determine height, flank slope, caldera depth, and volumes. Summit elevations range from 21.1 km to -0.5 km, and relief varies from 1.0 km to almost 22 km. Average flank slopes are in the range of <1¿ to ~10¿, consistent with basaltic shield volcanism. The very low slopes of highland patera are also consistent with pyroclastic volcanism. Minimum volumes range from <1012 to 1015 m3. Estimates of the time required to build these volcanoes, on the basis of long-term terrestrial eruption rates, range from hundreds of thousands to tens of millions of years.