The changing electricity market is increasing demands on the governing and overspeed protection systems that ensure safe operation and control steam turbines in conventional cycle, CCGT and CHP applications. Electricity generators are now coming under increasing commercial pressure to respond more rapidly to changes in grid load and frequency-regulating requirements. High-integrity systems are, therefore, required to monitor and control prime movers during rapid load transients affecting supply and demand. The necessary capacity for this rapid load changing is primarily provided by steam turbine plant, as much of the new gas-fired plant is limited in its ability to meet the need for flexible operation. This collection of seminar papers explores the effects of changing commercial and technical drivers upon the design, manufacture, operation and testing of steam turbine governing and overspeed protection systems.