Magnetic resonance contrast agents have demonstrated their clinical usefulness in a variety of organs for improved detection of various neoplastic, inflammatory and functional abnormalities. Gadolinium chelates are the most widely used. They are extracellular, non-specific contrast agents. Their use in many clinical indications is justified because, in conjunction with improved imaging techniques, these safe and image-enhancing contrast agents add morphologic and functional information compared with unenhanced MR images. This article describes the commercially available compounds, and summarizes their approval status on the international market regarding indications and doses. Their mechanisms of action, biodistributions, toxicities and tolerance profiles in normal and high-risk patient populations are described. Additionally, this article reviews the specific recommendations by the manufacturers for patients at risk. Finally, their main clinical applications are reviewed.