Book excerpt: Understanding caldera mechanisms, unrest and the danger of eruption is a crucial challenge for Earth sciences. Several key features of caldera behaviour have yet to be fully understood. The topics addressed in this volume include: the conditions required to produce and to release large volumes of magma erupted during caldera formation; how magmatic feeding systems evolve before and after a caldera has formed; the processes that limit the behaviour of precursors to eruptions; how pre-emptive precursors can be distinguished from those that drive unrest without an eruption.