The potential of mass spectrometry (MS) and gas chromatography/mass spectrometry (GC/MS) techniques for on‐site analysis of compounds in a variety of matrixes such as air, water, soil and surfaces is discussed. The fundamental principles of operation including different mass separation procedures, modes of injection and separation methods for mixtures are presented here with a special emphasis on equipment suitable for measurement in the field. Commercially available systems as well as prototypes are described in detail. The power of MS and/or GC/MS analyses on‐site compared with conventional methods carried out in the laboratory is demonstrated in a detailed review of the literature dealing with measurement campaigns and experiences when applying mobile MS and GC/MS. In conclusion, mobile mass spectrometers have reached a high standard of quality and the operational areas in which they are utilized are likely to increase considerably in the future.