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A review of the recent geochemical investigations carried out on products of the Campi Flegrei volcanic field is presented, with particular attention on radiogenic (Sr, Nd, Pb) and stable (B, O) isotope data. The studied volcanic rocks span the entire period of best known Campi Flegrei volcanic field activity, since ~58 ka to the last event, the AD 1538 Monte Nuovo eruption. The isotope data, combined with mineralogical, geochemical, geochronological and volcanological data have allowed reconstructing a complex behaviour of the Campi Flegrei volcanic field magmatic feeding system. They suggest that several, isotopically-distinct magmatic components fed the activity over various time periods. In particular, over the past 15 kyrs at least three isotopically-distinct magmatic components, located either in a deep and large reservoir or in shallower and smaller chambers, have variably interacted, eventually feeding the volcanic activity. These magmatic components originated through a complex interplay of magma supply from a variably-enriched mantle source, and crustal contamination processes occurring at depth. Mingling/mixing among these isotopically-distinct magmatic components, as well as closed-system differentiation of variable hybrid magmas and interaction with cumulate mushes, were the dominant processes acting in the Campi Flegrei caldera feeding system over the past 15 kyrs. Three examples including the Agnano-Monte Spina, Astroni and Averno 2 eruptions of this period are described to illustrate the interplay among the above-mentioned different processes.

Since the Late Pleistocene, Campi Flegrei have been inhabited by humans because of the region's soil fertility, mild climatic conditions, and both commercially and strategically advantageous position in the Mediterranean basin. After a period of frequent eruptions that affected the environment and forced indigenous farmers temporarily to abandon the area after each event, in 740 BC Campi Flegrei were chosen by Chalcidian Greeks from Ischia to establish the settlement of Cuma, which was the first Greek colony in what is today the Italian mainland. Since its earliest colonisation, the Phlegraean area, because of its location and environmental characteristics, has been a cause of conflicts over its control, and has also witnessed a significant increase in population and urban development. Even the threat of ongoing bradyseismic activity, which has caused seismicity and ground deformation, and the AD 1538 Monte Nuovo eruption did not discourage people from living in the area. Campi Flegrei have undergone socio-economic development which for most of its history has been sustainable. Only with industrialisation over recent decades, has it become unsustainable. This unsustainable development has also caused an increase in the vulnerability of the area in terms of its volcanic risk. Knowledge of the history of urbanisation in Campi Flegrei may, therefore, assist the civil authorities in effecting socio-economic policies aimed at disaster risk reduction.

The Campi Flegrei caldera is a complex and resurgent structure, and its active portion has been the site of an intense volcanism with eruptions concentrated in temporal clusters, called epochs. The caldera is home to about 350,000 people. In the past decades, many scientific studies were aimed at both defining fundamental parameters of a future eruption, and hazard zoning of the territory. The approach to the volcanic hazard assessment of the Campi Flegrei caldera has progressively changed through time from a “deterministic” interpretation of the available information to a quantitative probabilistic elaboration of the main sources of uncertainty. In particular, on the long-term, Astroni-Agnano-Solfatara is recognised to be the most probable area in which a vent will likely open, while the Averno-Monte Nuovo is the second most probable one. Significant uncertainty affects these results, and a non-negligible vent opening probability spreads over the whole caldera. The inter-event times of volcanic eruptions span from a few years to thousands of years. Within the epochs of activity, the mean recurrence time is tens of years, and intra-epoch temporal groups are evident. The probability that the next eruption will be of < 0.1 km3 volume of magma DRE is ~95%. Larger size eruptions tend to be localised in the central-eastern sector of the caldera. Expected hazards from renewal of explosive volcanism result from pyroclastic fallout and pyroclastic density currents. Pyroclastic fallout deposits in excess of 300 kg/m2 can affect most of the caldera and the city of Naples with more than 10% probability. The entire caldera has the potential to be affected by pyroclastic density currents invasion with mean probability above 30% in its central-eastern portion, and above 50% in the Agnano area. Invasion probabilities of ~5–10% have been estimated for the urbanised areas along the eastern slopes of the Posillipo Hill. In summary, probabilistic hazard assessment is particularly important in Campi Flegrei caldera, due to the uncertain location for potential vents and the large variability of eruption styles and sizes that cannot be, at the present time, effectively constrained by monitoring signals.