Warchalking is a wireless networking term that refers to the practice of drawing symbols, normally using chalk as a medium, in public places to demarcate or advertise a Wi-Fi wireless network that is open to the public.

The term was spawned as an analogy to the term "wardriving," which refers to the practice of navigating a given location in a vehicle to detect open Wi-Fi nodes and map them. "Wardriving," in turn, was a term coined from "wardialing," introduced in the 1983 movie WarGames as a term referring to the practice of dialing a list of telephone numbers sequentially to identify which ones were connected to fax machines or computers.

In June 2002, a group of friends came up with the warchalking concept and the various symbols for it, to later be publicized by London-based information architect and blogger Matt "Blackbelt" Jones. Jones was responsible for designing the set of symbols (which were inspired by hobo symbols, used to direct to each other where they could get a meal), and he produced a downloadable document containing them in addition to posting an online blog entry about warchalking.

In a matter of days, the concept of warchalking was discussed by numerous publications and television news programs worldwide. Matt Jones’ colleague, Ben Hammersley, created a well-known photograph of a warchalk symbol which is now well-known and has been widely reproduced.

The process of warchalking involves a person (known as the "warchalker") drawing a specific warchalk symbol, recognizable only to those in the know, on a wall, pavement or lamp post in the area of the Wi-Fi node. The providers of the Wi-Fi service may also practice warchalking themselves in order to advertise the availability of their Wi-Fi location, be it a personal or commercial location.

The practice did not become particularly popular despite its widespread coverage; instead, commercial enterprises offering Wi-Fi adopted and used the symbols in their logos and print advertisements as shorthand for Wi-Fi.

Warchalking originally consisted of three symbols. The first symbol, indicating an open Wi-Fi node, is of two half-circles with the open ends faced away from each other, and the words "SSID" (which is a Wi-Fi term that stands for "service set identifier") and "bandwidth" written above and below the symbol, respectively. The second symbol, indicating a closed Wi-Fi node, is of one circle with the word "SSID" written above it. The third symbol, indicating a Wired Equivalent Privacy (WEP) node, is of one circle with a large letter "W" at the center, and the words "SSID," "access contact" and "bandwidth" written to its upper-left, upper-right, and beneath it, respectively.