Power systems need to incorporate rising shares of intermittent renewables. The penetration levels of renewable energy sources, inverter-based resources and inverter-based loads have grown, which has negative impacts on the stability and system strength of existing power systems. System strength describes the ability to manage fluctuations in supply or demand while maintaining the voltage. Metrics for the system strength and the hosting capacity are needed, as well as ways to improve the strength, for example by managing the loads, electric vehicles, generation and grid-forming inverters. This book is intended to enable researchers to advance the movement towards smart grids and clean energy systems by providing solutions to improve system strength. Case studies underpin the technologies presented. Chapters cover power system strength assessment, voltage sensitivity-based metrics, high penetration of inverter-based resources and their impacts, dynamic model reduction of power networks, effects of power system strength on transmission capacity, control approaches for system strength, impact of renewables on voltage stability, and smart devices-based strategies for planning and operation. Power System Strength: Evaluation methods, best practice, case studies, and applications is a comprehensive book on power system strength in emerging power grids with high penetration of renewable energy systems, for researchers in university, academia and experts at utilities and power system operators.