  Due to their short lifetimes but their enormous energy release in all stages
of their lives massive stars are the major engines for the comic matter
circuit. They affect not only their close environment but are also responsible
to drive mass flows on galactic scales. Recent 2D models of radiation-driven
and wind-blown HII regions are summarized which explore the impact of massive
stars to the interstellar medium but find surprisingly small energy transfer
efficiencies while an observable Carbon self-enrichment in the Wolf-Rayet phase
is detected in the warm ionized gas. Finally, the focus is set on
state-of-the-art modelling of HII regions and its present weaknesses with
respect to uncertainties and simplifications but on a perspective of the
requested art of their modelling in the 21st century.
