This book describes the capabilities of nuclear techniques for elemental microanalysis in the biological field. A description of basic principles is given at the beginning, with special emphasis on X-ray Fluorescence, Rutherford Backscattering Spectrometry, Nuclear Reaction Analysis and Scanning Transmission Ion Microscopy. The major part of the volume is devoted to the applications in the life sciences and presents a general review of the subjects investigated during the last fifteen years. In addition, technical aspects of nuclear microanalysis in living tissues, including data processing and specimen preparation, are detailed. Examples of recent applications in cellular pharmacology, cell physiology and biomedicine are presented. The last part concerns the studies of unicellular micro-organisms involved in pollution problems. Postgraduate students and confirmed scientists will be able to find here basic information, references and practical aspects of this new tool, with in each case a comparison with other analytical techniques.