Searching for extraterrestrial civilizations

Three interrelated assumptions are critically examined in an attempt to outline a productive strategy for a search for extraterrestrial intelligence. Questions concerning the feasibility of interstellar travel are investigated. It is concluded that the probability of interstellar travel is high enough that, given a modest number of advanced civilizations, at least one of them will engage in interstellar voyages and colonize the galaxy. Assuming, however, that technological civilizations are rare the galaxy would be essentially unpopulated. Attention is given to the present lack of contact with extraterrestrial beings and frequencies for interstellar beacons.