The main objective of this monograph is to present the origins and the process of grammaticalization of periphrasis of motion verbs in Spanish which lasted until the seventeenth century, process which resulted in development of modoaspectual, modal, temporal and even discursive meanings. Furthermore, with the help of a relatively large corpus, which covers the major works written between the twelfth and seventeenth centuries, the author will try to discover the reasons that led to the final assessment of periphrasis in Spanish.