Taking Heine’s (2003) characterization of Grammaticalization as its point of departure, this paper proposes an elementary framework, and corresponding terminology, for the description of the most common types of historical change in grammar (changes in content, content syntax, expression, and morphosyntax) and the types of innovation that give rise to them (neologism, extension, adoption, reanalysis, monolingual and bilingual). These basic conceptual tools of the historical linguist are illustrated with an analytic account of the development of the Russian tense–aspect system, from prehistory through the attested period.