The Microscopic Imagers (MI) on the Mars Exploration Rovers, Spirit and Opportunity, have returned images of Mars with higher resolution than any previous camera system, allowing detailed petrographic and sedimentological studies of the rocks and soils. Designed to simulate a geologist’s hand lens, the MI cameras were mounted on the rovers’ instrument arms. They can resolve objects 0.1 mm across or larger. As part of the daily MER operations process, targets for the MI and other arm instruments were selected by using available Pancam, Navcam, and Hazcam imagery. The MI routinely observed targets that were investigated by the other ARM instruments to study surface details, to provide context for the spectrometer data, and to examine the results of rock abrasion tool (RAT) brushing and grinding activities (paraphrased from Ken Herkonhoff's Science article, Science vol 305, August 6, 2004).