The asymmetric rotor molecule methanol (CH3OH) has hundreds of transitions at centimeter-, millimeter-, and submillimeter wavelengths. Many of these are excited in the hot (T ≳ 150 K), dense (n ≳ 106 cm−3) molecular cloud cores surrounding newly formed massive stars or protostars. The high temperatures in these cores cause evaporation of icy grain mantles, releasing copious amounts of complex molecules, such as methanol, in the gas phase, which in hot cores has abundances (up to 10−6 relative to H2) that are two or more orders of magnitude higher than in cold dark clouds.