  The Magellanic System harbors >800 expanding shells of neutral hydrogen,
providing a unique opportunity for statistical investigations. Most of these
shells are surprisingly young, 2--10 Myr old, and correlate poorly with young
stellar populations. I summarize what we have learned about shell properties
and particularly focus on the puzzling correlation between the shell radius and
expansion velocity. In the framework of the standard, adiabatic model for shell
evolution this tight correlation suggests a coherent burst of star formation
across the whole Magellanic System. However, more than one mechanism for shell
formation may be taking place.
