  I review the evidence for the importance of feedback from massive stars at
small and large scales. The feedback mechanisms include accretion luminosity,
ionizing radiation, collimated outflows, and stellar winds. The good news is
that feedback doesn't entirely prevent the formation of massive stars, while
the bad news is that we don't know what does limit their masses. Feedback from
massive stars also influences their surroundings. I argue that this does not
produce a triggering efficiency above unity, nor does it prevent lots of prompt
star formation in GMCs, though it may preserve massive remnants of the clouds
for many dynamical times.
