Magnetic Resonance Imaging (MRI), as one of the most powerful methods in clinical diagnosis, has emerged as an additional method in the field of molecular and cellular imaging. Compared to established molecular imaging methods, MRI provides in vivo images with high resolution. In particularly in the field of cell-based therapy, non-invasively acquired information on temporal changes of cell location linked to high-resolution anatomical information is of great interest. Relatively new approaches like responsive contrast agents or MR imaging reporter gene expression are MRI applications beyond temporal and spatial information on labeled cells towards investigations on functional changes of cells in vivo. MRI-based cell monitoring and tracking studies require prior labeling of the cells under investigation for excellent contrast against the background of host tissue. Here, an overview is provided on contrast generation strategies for MRI of cells. This includes MR contrast agents, various approaches of cell labeling and MRI as well as MR spectroscopic methods used for cell tracking in vivo. Advantages and disadvantages of the particular labeling approaches and methods are discussed. In addition to description of the methods, the emphasis is on the potential but also challenges and shortcomings of this imaging technique for applications that aim to visualize cellular processes in vivo. (C) 2009 Elsevier Inc. All rights reserved.