Mass Spectrometry (MS) has a number of features namely sensitivity, high dynamic range, high resolution, and versatility which make it a very powerful analytical tool for a wide spectrum of applications spanning all the life science fields. Among all the MS techniques, MALDI Imaging mass spectrometry (MALDI MSI) is currently one of the most exciting both for its rapid technological improvements, and for its great potential in high impact bioscience fields. Here, MALDI MSI general principles are described along with technical and instrumental details as well as application examples. Imaging MS instruments and imaging mass spectrometric techniques other than MALDI, are presented along with examples of their use. As well as reporting MSI successes in several bioscience fields, an attempt is made to take stock of what has been achieved so far with this technology and to discuss the analytical and technological advances required for MSI to be applied as a routine technique in clinical diagnostics, clinical monitoring and in drug discovery.