This document discusses commonly used cementitious materials for concrete and describes the basic use of these materials. It is targeted at those in the concrete industry not involved in determining the specific mixture proportions of concrete or in measuring the properties of the concrete. Students, craftsmen, inspectors, and contractors may find this a valuable introduction to a complex topic. The document is not intended to be a state-of-the-art report, user's guide, or a technical discussion of past and present research findings. More detailed information is available in ACI 225R-99, "Guide to the Selection and Use of Hydraulic Cements," ACI 232.2R-03, "Use of Fly Ash in Concrete," ACI 233R-03, "Slag Cement in Concrete and Mortar," and ACI 234R-06, "Guide for the Use of Silica Fume in Concrete."