The impact of natural disasters has become an important and ever-growing preoccupation for modern societies. Volcanic eruptions are particularly feared due to their devastating local, regional or global effects. Relevant scientific expertise that aims to evaluate the hazards of volcanic activity and monitor and predict eruptions has progressively developed since the start of the 20th century. The further development of fundamental knowledge and technological advances over this period have allowed scientific capabilities in this field to evolve. Hazards and Monitoring of Volcanic Activity groups a number of available techniques and approaches to render them easily accessible to teachers, researchers and students. This volume reviews the different monitoring methods. It first considers fluids and solid products, approaches that provide valuable information on pre-eruptive processes and eruption dynamics. It also focuses on the description of geophysical monitoring methods under development.