This chapter describes the main features and components of the Structural Health Monitoring of historic buildings, including experimental campaigns (in which dynamic and environmental data are recorded), data processing, anomaly detection and nonlinear finite element simulations. The results of the dynamic monitoring campaigns conducted on three masonry towers in the historic centre of Lucca from 2015 to 2022 are then presented. The vibrations of the San Frediano bell tower, the Clock Tower and the Guinigi Tower were continuously monitored: high–sensitivity seismic stations were installed on the structures to record their response to the dynamic actions of the surrounding environment. The effects of natural and anthropic vibration sources on the dynamic behaviour of the towers were also investigated to detect novelties and anomalies that occurred during the monitoring period.