In the first 6 months of the Mars Reconnaissance Orbiter's Primary Science Phase, the High Resolution Imaging Science Experiment (HiRISE) camera has returned images sampling the diversity of volcanic terrains on Mars. While many of these features were noted in earlier imaging, they are now seen with unprecedented clarity. We find that some volcanic vents produced predominantly effusive products while others generated mostly pyroclastics. Flood lavas were emplaced in both turbulent and gentle eruptions, producing roofed channels and inflation features. However, many areas on Mars are too heavily mantled to allow meter-scale volcanic features to be discerned. In particular, the major volcanic edifices are extensively mantled, though it is possible that some of the mantle is pyroclastic material rather than atmospheric dust. Support imaging by the Context Imager (CTX) and topographic information derived from stereo imaging are both invaluable in interpreting the HiRISE data.