The use of glass-ionomer cements in clinical dentistry is now well established. They have a number of unique properties, including adhesion to moist tooth structure, biological compatibility, and anticariogenic properties due to their fluoride release. Their use in treating early carious or erosion lesions has been widely investigated. Established techniques include fissure filling and sealing, restoration of class 5 erosion lesions without cavity preparation, and the internal occlusal fossa or tunnel restoration. The "sandwich" technique using glass-ionomer cements as "dentin substitutes" has enabled composite restorations to be used with greater safety where pulpal damage may occur. The future probably lies in using a laminate technique where materials that attach to dentin and form a biological seal can be covered by tougher and harder enamel veneers, thus mimicking the structure of the tooth. The deficiencies of glass-ionomer cements are well known, including lack of toughness, early water sensitivity, low abrasion resistance, and porosity leading to poor surface polish. Solving these problems is formidable, since inherently the strength of these cements is related to their water content. The clinician should be aware of these deficiencies and stay within the parameters of the techniques outlined in this paper. In particular, clinical success depends upon early protection of the cement from hydration or dehydration, and the current use of light-cured bonding agents has largely solved this problem.