This paper describes the digital processing performed by the Image Processing Laboratory (IPL) of the Jet Propulsion Laboratory (JPL) on the images of Mercury returned to earth from Mariner 10. Each image contains considerably more information than can be displayed in a single picture. Several specialized processing techniques and procedures were utilized to display the particular information desired for specific scientific analyses: radiometric decalibration for photometric investigations, high-pass filtering to characterize morphology, modulation transfer function (MTF) restoration to provide the highest possible resolution, scene-dependent filtering of the terminator images to provide maximum feature discriminability in the regions of low illumination, and rectification to cartographic projections to provide known geometric relationships between features. A principal task was the construction of full disk mosaics as an aid to the understanding of surface structure on a global scale; the detailed steps involved in the production of pictures for these mosaics are descibed.