THIS CHAPTER DISCUSSES THE APPLICATION AND provides some insight into the background of the test procedures for the basic aggregate properties of bulk density, relative density (specific gravity), absorption, and surface moisture. It is substantially a revision of the work of Landgren [1] in ASTM STP 169C, with an update of the terminology and the addition of a discussion on the importance of pore structure. The information from the original article by Timms [2] in ASTM STP 169 and the revised articles by Brink and Timms [3] in ASTM STP 169A and by Mullen [4] in ASTM STP 169B remains pertinent and is included in the chapter.