The AllWISE program builds upon the work of the successful Wide-field Infrared Survey Explorer mission (WISE; Wright et al. 2010) by combining data from the WISE cryogenic and NEOWISE (Mainzer et al. 2011 ApJ, 731, 53) post-cryogenic survey phases to form the most comprehensive view of the full mid-infrared sky currently available. By combining the data from two complete sky coverage epochs using an advanced data processing system, AllWISE has generated new products that have enhanced photometric sensitivity and accuracy, and improved astrometric precision compared to the 2012 WISE All-Sky Data Release. Exploiting the 6 to 12 month baseline between the WISE sky coverage epochs enables AllWISE to measure source motions for the first time, and to compute improved flux variability statistics. The AllWISE Atlas Metadata Table contains brief descriptions of all metadata information that is relevant to the production of the Atlas images and Source Catalog. The table contains the (RA, DEC) of the center of the Tile. Much of the information in this table is processing-specific and may not be of interest to general users (e.g., flags indicating whether frames have been processed successfully or not, and the date and time of the start of the pipeline processing, etc.). The metadata table also contains some characterization and derived statistics of the coadd image Tile, basic photometric parameters used for photometry and derived statistics for extracted sources and artifacts.