Radioactive Isotopes, Particularly in the Form of Radiotracers and Radioactive Sealed Sources, Have Been Used over a Broad Spectrum of Process Industries for Equipment and Process Troubleshooting, Monitoring, Control, Inspection, Optimisation and Many Other Purposes. Radioisotope-Based Measurement Techniques Are Best Suited for Multiphase Flow Systems Encountered in Industrial Processes, Since These Systems Are Opaque and Contain a Large Volume Fraction of the Dispersed Phase. in This Manuscript, Some of These Techniques and their Applications Are Outlined and Discussed. © 2009 Inderscience Enterprises Ltd.