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 group had its call for interest in November 2006, and the official standards task force was authorized in May 2007. The IEEE ratified the final standard in September 2010. Some companies introduced technology to reduce the power required for Ethernet before the standard was ratified, using the name Green Ethernet.

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 by the physical layer as transmitters are active regardless of whether data is being sent. If they could be put into sleep mode when no data is being sent, that energy could be saved. When the controlling software or firmware decides that no data needs to be sent, it can issue a low-power idle (LPI) request to the Ethernet controller physical layer PHY. The PHY will then send LPI symbols for a specified time onto 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 predetermined period of time. The data link is considered to be always operational, as the receive signal circuit remains active even when the transmit path is in sleep mode.