  This review covers the dynamic processes that are important in the evolution
and structure of galactic HII regions, concentrating on an elementary
presentation of the physical concepts and recent numerical simulations of HII
region evolution in a non-uniform medium.
  The contents are as follows:
  (1) The equations (Euler equations; Radiative transfer; Rate equations; How
to avoid the dynamics; How to avoid the atomic physics).
  (2) Physical concepts (Static photoionization equilibrium; Ionization front
propagation; Structure of a D-type front; Photoablation flows; Other
ingredients - Stellar winds, Radiation pressure, Magnetic fields,
Instabilities).
  (3) HII region evolution (Early phases: hypercompact and ultracompact
regions; Later phases: compact and extended regions; Clumps and turbulence).
