Interferometry of red supergiants before 2000: The M2 supergiant Betelgeuse (α Ori) is the first star whose angular diameter was measured by the Michelson stellar interferometer (Michelson & Pease 1921). Since then, however, we had to wait half a century before we witnessed the renaissance of interferometric observations in optical astronomy with novel methods such as speckle interferometry (Laberie 1970). Michelson's classical method was also extended to the infrared regime (e.g. McCarthy et al. 1977). The initial results served not only to compare stellar temperature scale with the measured angular diameters but also to probe scattering and thermal emission in the dust envelope around red supergiant stars (e.g. Tsuji 1978,1979). Interferometry has been more active in the radio domain: In connection with our subject, VLBI observations revealed many masering water clouds around red supergiants such as VY CMa (Imai et al. 1997) and S Per (Richards et al. 1999), but their origin in unknown. Also, radio observation of Betelgeuse with the VLA (Lim et al. 1998) revealed the presence of a new component of modest temperatures (Tex ≲ 3500 K) over the same height range as the classical chromosphere (Tex ≳ 5000 K), but again the nature of the new component remains obscure.