While the modern data center still contains a mixture of different application-specific networks and protocols, various types of Ethernet have emerged as the preferred approach for many data networking problems. With the addition of new industry standard extensions that permit lossless transmission, converged enhanced Ethernet (also known as lossless Ethernet) is now widely available. New applications have emerged, such as the convergence of networking and storage through Fibre Channel over Ethernet, remote direct memory access over Ethernet (iWarp), and the use of Ethernet to supplement or replace conventional interconnects between data centers (metro Ethernet and related efforts). This chapter will provide an overview of Ethernet protocols, including both classic versions and more recent updates targeted for data center applications.