Hundreds of thousands of earthquakes occur worldwide each year, but most of them go unnoticed. Only a few are very destructive. Most earthquakes have a tectonic origin and happen in well-defined, relatively narrow seismic zones. ‘Seismicity—the restless Earth’ first describes the elastic rebound model that explains how an earthquake occurs. There are two measures of the size of an earthquake: its magnitude and intensity. Magnitude is a measure of the energy released by the earthquake classified by the Richter scale, while intensity is a qualitative measure based on observed effects using a twelve-part scale. Maps of the locations of earthquake epicentres show that these are concentrated in narrow seismically active zones. Earthquake monitoring and prediction are discussed.