Wake-on-LAN (WoL) is an Ethernet or Token Ring computer networking standard that allows a computer to be turned on or awakened from sleep mode by a network message. The message is usually sent to the target computer by a program executed on a device connected to the same local area network (LAN). It is also possible to initiate the message from another network by using subnet directed broadcasts or a WoL gateway service. It is based upon AMD's Magic Packet Technology, which was co-developed by AMD and Hewlett-Packard, following its proposal as a standard in 1995. The standard saw quick adoption thereafter through IBM, Intel and others.

If the computer being awakened is communicating via Wi-Fi, a supplementary standard called Wake on Wireless LAN (WoWLAN) must be employed. The WoL and WoWLAN standards are often supplemented by vendors to provide protocol-transparent on-demand services, for example in the Apple Bonjour wake-on-demand (Sleep Proxy) feature.

The basis for the Wake-on-LAN industry standard mechanism today was created around 1994 by AMD in cooperation with Hewlett-Packard, who co-developed AMD's Magic Packet Technology and brought forth their following proposal for it in November 1995 in an AMD white paper. It enabled a remote network device to be woken up through the underlying “power management circuitry”, by sending it a standard Ethernet frame, which “contains a specific data pattern detected by the Ethernet-controller on the receiving end”.

AMD implemented the WoL mechanism in their AMD PCnet II-Family of Ethernet controllers before. The term “Magic Packet” is a AMD trademark.

Wake-on-LAN saw wide adoption starting in October 1996, when IBM formed the Advanced Manageability Alliance (AMA) with Intel. In April 1997, this alliance adopted the Wake-on-LAN technology.

Contrary to most networking protocols, no formal Request for Comments (RFC) documents have been created for Wake-on-LAN, but nevertheless it remains a standard that is widely used in the industry.

Ethernet connections, including home and work networks, wireless data networks, and the Internet itself, are based on frames sent between computers. WoL is implemented using a specially designed frame called a magic packet, which is commonly sent to all computers in a network, among them the computer to be awakened. The magic packet contains the MAC address of the destination computer. This is an identifying number, built into each network interface controller (NIC), that enables the NIC to be uniquely recognized and addressed on a network. In computers capable of Wake-on-LAN, the NIC(s) listen to incoming packets, even when the rest of the system is powered down. If a magic packet arrives and is addressed to the device's MAC address, the NIC signals the computer's power supply or motherboard to awaken. This has the same effect as pressing the power button.

The magic packet is broadcast on the data link layer to all attached devices on a given network, using the network broadcast address; the IP address (which relates to the internet layer) is not used. Because Wake-on-LAN is built upon broadcast messaging, it can generally only be used within a subnet. Wake-on-LAN can, however, operate across any network in practice, given appropriate configuration and hardware, including remote wake-up across the Internet.