Passive optical networks (PONs) are a fiber-optic access technology that can be used for residential and business access, and also for certain backhaul applications and data communications. These applications are also referred to as FTTX, where X stands for H (Home), B (Building), C (or Curb), or Cab (Cabinet). This chapter describes PON technology, including optical access networks as defined in ITU-T Recommendations G.902, G.983, and SG15, and other standards. PON variants are described, including GPON, EPON, APON, BPON, XG-PON, and FSAN. Upstream and downstream access technologies are discussed, including TDMA and WDMA. Wavelength multiplexing technology for PONs is also discussed, and examples are given, including Verizon FiOS.