The contemporary state of the problem of molecular masers observed In regions of active star formation is briefly reviewed. The major landmarks of the history of their discovery, observations,
and interpretations are mentioned. OH masers observed In these regions are believed to be a product of disintegration of dense
molecular envelopes ("cocoons") surroundlng compact HlI regions of young OB-stars. They are local ized at, typically, =:10^17 cm from their parent star and have there densities = 10^6 cm, temperatures
=100 K, magnetic fields of the order of several mG. At least in some cases they seem to be falling on the star.
H2O (and, as an exception, Si0) masers are connected with still earlier stages of stellar evolutlon, when a very strong mass loss from the saár (up to =10^-3 - 10^-2 M /yr) takes place. H2O maser emission is produced by gas-dynamical (possibly MHD) interaction between the stellar wind and the surroundlng gas.The H2O sources may be localized much closer to their stars than the OH sources, - up to =10^14 - 10^15 cm, and they indicate much higher densities (=-10^11 cm^-3) and magnetic fields (up to several G), and higher temperatures ( = 100 - 1000 K). They reveal also rather llvely klnematics of the circumstellar gas (up to several hundred km/s).
CH3OH 1.3 cm low-gain masers in Orion with their observed dimensions and derived densities and temperatures may be gravitationally unstable and, with their posltion around a
pre-Trapezium young star cluster, may perfectly be a group of protostars. Much stronger CH3OH 2.5 cm masers, recently discovered in the direction of many compact HII regions, are dosely associated with the OH masers.