"The application of alkali-metal ion or atomic beams to the diagnostics of magnetically confined plasmas has a long history. Thermionic ion sources are used mostly because of their ease of handling. Fine probing beams and rather large atomic collision cross sections provide good spatial and temporal resolution of the measurements. Among the variety of this kind of diagnostics, two methods are reviewed as typical examples : a heavy ion beam probe (HIBP) and beam probe spectroscopy using a neutral lithium beam (LiBP)."