Owing to the unique spatio-chemical information provided by MSI, a number of techniques, primarily differing in their approach to analyte desorption/ionization, have emerged to broaden the application and improve the performance of MSI in various research fields. The sample preparation and analyte desorption/ionization methods, mass analyzers, and other technologies used impact the results one obtains; thus, it is important to have a basic understanding of the available approaches when choosing the one most appropriate for an experiment. Consider also that many companies and universities will often have more than one MS system, and the recommendations provided by the staff will depend not only on the samples and data required by a user, but also on instrument availability. In the following sections we describe the fundamentals of several ionization techniques (also listed in Table 1), in roughly the order of their potential application to food science.