Differential protection is a fast, selective protection method used in various applications for electrical machines, transformers, busbars, and lines. This book provides the fundamental principles of differential protection in both analog and digital technology. Special chapters are dedicated to the behavior and sizing of current transformers, as well as modern digital communication for line protection. The different variants of differential protection are described in detail, with practical applications illustrated through specific examples. This is complemented by recommendations for commissioning, testing, and maintenance. The entire design and management of modern differential protection is explained using the current Siemens SIPROTEC protection relays. Serving as both a textbook and a standard reference, the book covers all topics that need to be considered during planning and project execution.