The term "earthquake early warning" (EEW) is used to describe real-time earthquake information systems that have the potential to provide warning prior to significant ground shaking. This is possible by rapidly detecting the energy radiating from an earthquake rupture and estimating the resulting ground shaking that will occur later in time either at the same location or some other location. Warning times range from a few seconds to a little more than a minute and are primarily a function of the distance of the user from the earthquake epicenter. The concept has been around for as long as we have had electric communications (e.g., Cooper 1868), but it is only in the last two decades that the necessary instrumentation and methodologies have been developed (e.g., Nakamura 1988; Espinosa-Aranda et al. 1995). The last five years in particular have seen a rapid acceleration in the development and implementation of EEW, fueled by a combination of seismic network expansion, methodological development, and awareness of the increasing threat posed by earthquakes paired with desire by the seismological community to reduce risk.