This book is aimed at understanding the concepts and methodologies involved in the recent Passive Optical Networks (PONs) which have evolved to provide much higher bandwidth at the lowest cost in the access networks. The WDM optical systems have totally revolutionized the telecommunication sector by opening up a new dimension in networking.A PON is a system that brings optical fiber cabling and signals to the end user employing multiple wavelengths in a single fiber to multiply the capacity without increasing the data rate thus offering better privacy and scalability because each Network Unit receives its on wavelength.WDM-PON is the next generation in development of access networks. The book presents a brief overview and benefits of WDM-PON over conventional PON technologies. It also focuses on various WDM-PON applications, advantages, disadvantages and its challenges . It illustrates the simulation of WDM- Passive Optical Network for different data formats, bit rates, signal input power and extinction ratio. I shall feel my labour amply rewarded if this book proves to be useful to graduate students as well as scientists and engineers involved in lightwave technology