  Mechanical feedback from massive stars, primarily from supernovae, can
dominate ISM structuring and phase balance, thereby profoundly affecting
galactic evolutionary processes. Our understanding of mechanical feedback is
based on the adiabatic, wind-driven bubble model, applied on size scales
ranging over three decades. Tests of the model, and our consequent
understanding of feedback, are reviewed. While the model is broadly successful,
critical unknowns still prevent a comprehensive understanding of the
consequences of feedback.
