A great deal of the material in this chapter is based on the work of the authors in the two previous editions of ASTM STP 169. D. L. Bloem authored the section on soundness and deleterious substances in ASTM STP 169A and L. Dolar-Mantuani did the chapter of the same name in ASTM STP 169B. I am indebted to them for their earlier work, most of which remains very valid today. For ASTM STP 169C, the subject of aggregate coatings is grouped with soundness and deleterious substances in this chapter. The discussion of coatings by M. A. Ozol in ASTM STP 169B was used as a basis for die inclusion on that subject here. In contrast to previous editions, the chapter has been organized to concentrate on relevant ASTM standards and their use in dealing with these three aspects of aggregate quality.