Undersea Fiber Communication Systems, Third edition is an authoritative guide exploring the comprehensive aspects of optical communication systems over submarine cables. Covering topics such as design, technology, installation, and maintenance, it serves as an essential resource for students, experts, operators, and investors alike. This updated edition reflects the significant advancements made in the field over the past decade, ensuring it remains indispensable in the rapidly evolving domain of submarine optical communications. The third edition addresses key developments including the transverse role of open cables, the evolution of coherent transponders, and the impacts of space division multiplexing (SDM). The book also explores advancements in wet plant equipment, environmental impacts of marine operations, contract management, and the progression of unrepeated systems to match repeated systems at network levels. This comprehensive update ensures the book's relevance and utility in a field marked by continuous innovation.