The monograph examines the history of two main types of Indo-European conjugation in Slavic, Baltic and ancient Balkan languages. The reflection of the atematic type of conjugation is established, its expansion in different periods of development of these dialect groups and the subsequent gradual death. The presence of regular correspondences between the second Indo-European series of verbs and verbs for a long vowel in Baltic and Slavic is revealed. The boundaries of the Augmented Area and the chronology of the formation of a sigmatic aorist are investigated . Syntactic Origins of Slavic Species Oppositions . Reconstructed a number of common for Baltic and Slavic species combinations of verbs with syntactic particles and preverbs.