AWAIC: A WISE Astronomical Image Co-adder Frank J. Masci, John W. Fowler, Roc M. Cutri The Wide-field Infrared Survey Explorer (WISE) is a NASA Midex mission launching in late 2009 that will survey the entire sky at 3.3, 4.7, 12, and 23 microns with sensitivities up to three orders of magnitude beyond those achieved with IRAS. One of its products is a digital Image Atlas that will combine survey exposures within predefined tiles on the sky. To support this, we have developed a generic frame co-addition tool, AWAIC, for execution in the automated pipeline. Here we describe AWAIC's algorithms, functionality, and products. The software includes preparatory steps such as frame background matching and outlier detection. Frame co-addition is based on using the detector's Point Response Function (PRF) as an interpolation kernel. This kernel reduces the impact of prior-masked pixels; enables the creation of an optimal matched filtered product for point source detection; and most important, it allows for resolution enhancement (HiRes) to yield a "model" of the sky that is consistent with the observations within their uncertainties. This is accomplished through a Richardson-Lucy like procedure, extended to include non-isoplanatic PRFs, prior noise weighting, variance estimation, and ringing-artifact suppression. HiRes is not in the WISE automated processing plan. Ancillary products include images of uncertainties, depth-of-coverage, and outlier locations. AWAIC supports the FITS standard with all common projections and coordinate systems, and will be made portable in the near future.