Since 1949 the techniques have included lexicostatistic glottochronology. In spite of its impressive technical name, it is in essence basically simple. This chapter explains what it is, how it used, up to what point the validity of its findings have been established, its imperfections, and the possibilities for correcting its deficiencies and converting it into a precise instrument. Glottochronology, formed from “chronology” prefixed by Greek glotta, language, is the sequence in which stages in the history of a language have appeared or the history of the separation of a language into local dialects, and the differentiation of these in a more or less gradual fashion into distinct languages. Glottochronology exists only as part of the established science of comparative linguistics. Lexicostatistic glottochronology has been criticized for the disparity between the maximum and minimum limits of the range of retention, with the claim that after many centuries the error can reach enormous proportions.