  The discovery of the first naturally occurring high gain hydrogen
recombination line (HRL) maser, in the millimeter and submillimeter spectrum of
the emission line star MWC349, requires an expansion of current paradigms about
HRLs. In this paper we re-examine in general the physics of non-LTE populations
in recombining hydrogen and specify the conditions necessary for high-gain
masing and lasing in HRLs.
  Saturation of masing recombination lines is a critical consideration.
  We draw attention to another non-LTE phenomenon active in hydrogen: the
overcooling} of populations. Observationally the HRL overcooling might manifest
itself as an anomalously weak emission recombination line, or as a ``dasar,''
that is, an anomalously strong absorption line.
  We briefly discuss the prospects of detecting hydrogen masers, lasers and
dasars in several classes of galactic and extragalactic objects, including
compact HII regions, Be or Wolf-Rayet stars, and AGNs.
