This research work is dealt with the analysis of the decline of the native speaking population, specifically the case of Quechua, since it was historically the most spoken language in Peru, but currently only a minority of people speak it._x000D_ The aim of this research is to prove that the Quechua language has been declining over the years, to provide with suggestions to preserve it, since it is part of our national culture._x000D_ Thanks to the collection of information of the censuses of the last years and interviews, we could conclude that the Quechua-speaking population of Peru has not been steadily declining in recent years, according to the censuses of 1940, 1961, 1972, 1993 and 2007. The Quechua language has declined notoriously according to the censuses of 1940, 1961 and 1972, in contrast to the increasing of the population; but from the census of 1993 this reduction is neither...