THE FIRST EDITION OF THE CHAPTER ON “CHEMICAL Admixtures” was issued in 1966 and was prepared by Dr. Bruce Foster [1]. The chapter in ASTM STP 169B [2], published in 1978, was an updating of Dr. Foster's paper prepared by Bryant Mather. In 1994, the chapter was again updated by Bryant Mather and appeared in ASTM STP 169C [3]. In the preparation of this chapter, the contents of the previous editions were drawn upon and some duplication of information from the previous edition exists. We acknowledge the authors of the previous editions and their contributions to the literature on this topic. The current edition will update the topics addressed previously, provide up to date references, and focus primarily on new technologies that have been developed. The review period has been limited to contributions made during the last decade. Attempts have been made to uncover all relevant research, but undoubtedly, important research may not be covered or may be unknowingly omitted in this review.