Across the world, change is accelerating in power systems driven by the advent of low-cost, abundant wind and solar energy, the rise of distributed energy resources and increasing digitalization. These factors are leading to a structural shift in the way power systems are best planned and operated. In particular, they call for increased flexibility of power systems. Power system flexibility encompasses all relevant characteristics of a power system that facilitates the reliable and cost-effective management of variability and uncertainty in both supply and demand. A lack of system flexibility can reduce the resilience of power systems, or lead to the loss of substantial amounts of clean electricity through curtailment of VRE. Power plants play a critical role in enhancing system flexibility. Based on a wealth of real-life case studies and data, this report provides a comprehensive overview of how power plants can contribute to making power systems more flexible, while enhancing electricity security. It summarises the findings of the Advanced Power Plant Flexibility (APPF) campaign of the Clean Energy Ministerial (CEM). The solutions presented in this study have been collected in close collaboration with industry stakeholders, including manufacturers, expert consultancies, system operators and plant operators.