Energy-Efficient Ethernet (EEE) is a set of enhancements to the twisted-pair and backplane Ethernet family of computer networking standards that reduce power consumption during periods of low data activity. The intention is to reduce power consumption by 50% or more, while retaining full compatibility with existing equipment. The Institute of Electrical and Electronics Engineers (IEEE), through the IEEE 802.3az task force developed the standard. The first study was held in May 2007. The IEEE ratified the final standard in September 2010. Some companies introduced technology to reduce the need for Ethernet before the standard was ratified, using the name Green Ethernet.

In 2005, all the network interface controllers in the United States (in computer, switches, and routers) used an estimated 5.3 terawatt-hours of electricity. According to a researcher at the Lawrence Berkeley Laboratory, Energy-Efficient Ethernet can potentially save an estimated US $ 450 million in US $ 200 million, and offices ($ 170 million), and the remaining $ 80 million from data centers.

The power reduction is accomplished in a few ways. In Fast Ethernet, Gigabit Ethernet and 10 Gigabit Ethernet links, constant and significant energy is used. If they could be put into sleep when it was not safe, that energy could be saved. When the controlling software or firmware decides that it needs a low-power idle (LPI) request to the Ethernet controller physical layer PHY. The PHY will then send LPI symbols for a specified time on the link, and then disable its transmitter. Refresh signals are sent periodically to maintain link signaling integrity. When there is data to transmit, a normal IDLE signal is sent for a period of time. The data link is considered to be operational,

Some energy-efficient switch-integrated circuits were developed before the IEEE 802.3az standard was finalized. Green Ethernet technology was a superset of the 802.3az standard. Energy-Efficient Ethernet, Green Ethernet works in one of two ways. First, it detects a link to the status quo, where it is connected to the power of a computer, and is not active. Second, it detects cable length and adjusts the power accordingly. Previous standard switches provide enough power to send a signal up to. However, this is often unnecessary, especially in the home, where cabling are typical between rooms. In addition to the pure power saving benefits of Green Ethernet, backing off the shorts and improving the overall performance of the cabling system. Green Ethernet also encompasses the use of more efficient circuits in Ethernet chips, and the use of “off-load engines” on Ethernet interface cards intended for network servers.

In April 2008, the term was used for switches, and, in July 2008, used with wireless routers which featured user-selectable off periods for Wi-Fi to further reduce energy consumption.

Green Ethernet was first used on home products. However, low port counts mean that significant cost savings are not going to be made using this technology only in the home. They are more likely to provide a more immediate saving. Projected power savings of up to 80 percent were estimated using Green Ethernet switches, translating into a shorter product life due to reduced heat dissipation.