Publisher Summary This chapter reviews the various passive optical network (PON) architectures and technologies. It paves the way for understanding the reasons and philosophies behind the PON technology development. PON has become an import access technology for next generation broadband services. It offers long-reach and high-bandwidth passive local loops using single-mode optical fiber. A PON network is characterized by a passive remote terminal (RT). There are two major ways to realize a passive distribution plant: power splitting (TDM-PON) and wavelength multiplexing (WDM-PON). Time division multiplexing is used for multiplexing data from different ONUs on a power-splitting PON. A ranging process is required to set up ONUs at different transmission distances from the OLT with a common logical timing reference, which is used in scheduling ONU transmissions. In a power-splitting PON, the PON bandwidth is shared among ONUs. Power budget eventually limits the speed, distance, and ONU count in a power-splitting PON. A WDM-PON provides an upgrade path to overcome the limitations of a power-splitting PON. In a WDM-PON, a WDM multiplexer is used at the RT to combine the signals from different ONUs. The WGR is an important optical element for WDM-PON remote nodes. It enables many scalable and flexible WDM-PON designs. By using CWDM technology on a PON infrastructure, one can reuse the fiber plant infrastructure through different FSRs in a WDM-PON or overlaying multiple PON. The low loss, low noise, and exceptionally large bandwidth of optical fiber make it ideal for long-distance backbone network transmission.