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[[File:Dr. Frank Drake.jpg|thumb|Dr. [[Frank Drake]]]]

The '''Drake equation''' is a [[probability theory|probabilistic argument]] used to estimate the number of active, communicative [[extraterrestrial life|extraterrestrial civilizations]] in the [[Milky Way]] [[Galaxy]].<ref name="Burchell"/><ref>{{cite journal |last1=Glade |first1=N. |last2=Ballet |first2=P. |last3=Bastien |first3=O. |date=2012 |title=A stochastic process approach of the drake equation parameters |journal=[[International Journal of Astrobiology]] |volume=11 |issue=2 |pages=103–108 |arxiv=1112.1506 |bibcode=2012IJAsB..11..103G |doi=10.1017/S1473550411000413|s2cid=119250730 }}</ref>

The equation was formulated in 1961 by [[Frank Drake]], not for purposes of quantifying the number of civilizations, but as a way to stimulate scientific dialogue at the first scientific meeting on the [[search for extraterrestrial intelligence]] (SETI).<ref name='December 2002'>{{cite web |date=December 2002 |title=Chapter 3 – Philosophy: "Solving the Drake Equation |url=http://www.setileague.org/askdr/drake.htm |work=Ask Dr. SETI |publisher=SETI League  |access-date=2013-04-10}}</ref><ref>{{cite web |last=Drake |first=N. |date=30 June 2014 |title=How my Dad's Equation Sparked the Search for Extraterrestrial Intelligence |url=http://news.nationalgeographic.com/news/2014/06/140630-drake-equation-50-years-later-aliens-science/ |work=[[National Geographic (magazine)|National Geographic]] |access-date=2 October 2016}}</ref> The equation summarizes the main concepts which scientists must contemplate when considering the question of other radio-communicative life.<ref name='December 2002'/>  It is more properly thought of as an approximation than as a serious attempt to determine a precise number.

Criticism related to the Drake equation focuses not on the equation itself, but on the fact that the estimated values for several of its factors are highly conjectural, the combined multiplicative effect being that the uncertainty associated with any derived value is so large that the equation cannot be used to draw firm conclusions.