This volume provides a comprehensive presentation of counting networks - a fundamental class of distributed data structures providing efficient solutions to important problems in distributed systems. Specifically, counting networks solve distributed coordination problems such as counting, load balancing, and barrier synchronization. Among other topics, this book provides constructions of counting networks, examines their limitations as well as their ability to support additional functionalities, and evaluates several measures of performance for counting networks. The main purpose of the book is to make the most important results on counting networks accessible to a wide audience and to stimulate new research on this fascinating topic. "Counting Networks" is suitable as a text in advanced-level courses specialized in distributed computing with networked data structures. The book will also be a useful tool for the practitioner who implements distributed data structures for distributed system applications.