Fiber optics has become the backbone of all communications systems, including telecom - landline and wireless - the Internet, CATV, LANs, etc. All these fiber optic networks require testing to ensure they are installed properly and to troubleshoot problems when they arise. Fiber optic manufacturers and network users say that testing is the most important aspect of installation and operation but often the least well understood. This book has been written by the FOA to provide a comprehensive but understandable technical guide to this important topic. The Fiber Optic Association, Inc. (FOA) was founded in 1995 by a group of instructors who were highly experienced at teaching fiber optics. They represented educational institutions, manufacturers and commercial and government users of fiber optics, including all types of fiber optic applications. All were concerned about the absence of standards for teaching fiber optic technicians and industry certifications to show their competence. The FOA was chartered to promote fiber optics through education, certification and standards. Today the FOA is recognized around the world as the authority on fiber optic training and certification. The FOA has always tried to provide the world with sources of technically correct unbiased information on fiber optics using both print and electronic media. For such a broad subject as testing fiber optic networks, we depend on the FOA Online Reference Guide on the FOA website (www.foa.org), the largest and most widely used reference on fiber optics to supplement the material in this book. This book and the FOA Online Reference Guide provide a basic reference for testing fiber optic networks and a study guide for FOA Fiber Optic Specialist Certification in testing.