High Quality Content by WIKIPEDIA articles! The 10/40 Window is a term coined by Christian missionary strategist Luis Bush in 1990 to refer those regions of the eastern hemisphere, plus the European and African part of the western hemisphere, located between 10 and 40 degrees north of the equator, a general area that in 1990 was purported to have the highest level of socioeconomic challenges and least access to the Christian message and Christian resources on the planet.