In this paper, the authors present the reasons for, and the subsequent development of, systems for the regular monitoring of movement in historic structures. A major program of repair and structural reinforcement to the supports of the dome took place at St. Paul's Cathedral between 1923 and 1935 and from that period onwards, precise observations of the foundation levels have been recorded annually. At that time a system of crack measurement was instituted employing pairs of bronze pins set into the masonry spanning settlement cracks and measured by instruments designed by the son of the legendary Charles Darwin. Records indicated that a lateral displacement in the south transept was occurring. In order to measure this movement, a clock micrometer was installed in the north wall of the transept and readings were taken daily. The results obtained from this experimental installation demonstrated the value of regular and frequent readings. This led to the preparation of a specification for an automatic monitoring system which would provide frequent and accurate data from a number of locations within the south transept. Due to the system's success, further development work was undertaken to implement similar measurement programs at Chichester Cathedral, the Church of St. Stephen's, Walbrook, and several large secular buildings. An additional system was also installed at St. Paul's Cathedral to measure lateral movement between the two western towers. This was achieved by installing twinned wires between the towers and connecting them to an array of four transducers producing printed data for subsequent processing and graphing by computer.