A mesoscale convective system (MCS) is an organised grouping of thunderstorms reaching an extent of 100 km or more and persisting for at least 6 hours, behaving as a coherent meteorological entity. MCSs are responsible for a significant proportion of extreme precipitation and flooding at mid-latitudes and in the tropics, producing rainfall accumulations that can exceed 200 mm in just a few hours. Several types are distinguished: the mesoscale convective complex (MCC), nearly circular in infrared satellite imagery with a cold cloud shield exceeding 100,000 km²; the squall line, with linear arrangement; and intermediate forms. Formation requires a combination of atmospheric instability (high CAPE), abundant low-level moisture, a triggering mechanism (front, convergence, orography), and vertical wind shear to organise convection. In the western Mediterranean, MCSs are the main drivers of catastrophic torrential rainfall: the Valencia floods of October 2024, and numerous DANA events are products of MCSs fed by moisture from the warm Mediterranean. Ensemble prediction and high-resolution models have substantially improved anticipation of these systems, though the exact location of maximum rainfall remains difficult to pinpoint more than 24 hours in advance.