The Slavic languages are fusional. Categories include person, gender, number, tense, aspect, and mood. We concentrate on endings for non-past, compound tenses, aorist, imperfect, and imperative, starting from Proto-Slavic (PSL), with reference to Proto-Indo-European (PIE). The time lapse between PIE and PSL is vast, so details are largely unrecoverable. The situation in the modern Slavic languages is sketched, summarizing secondary and primary endings, roots, themes, and thematic and athematic formations. The PIE present, aorist, and optative are outlined. Morphological persistence, innovation, and loss are evident from the data, and analogy plays an important and expected role. Attention is drawn to uncertainties in the origins of the various endings, uncertainties which on the whole have been pointed out, though much is open to research and discussion. Overall, the general state of the art in the field is well-established, but there is scope for further investigation, as becomes even clearer once viewed alongside other chapters.

This chapter presents the processes that have resulted in dialectal fragmentation of Slavic languages. It starts with a discussion of early differences in Proto-Slavic, most notably those in reflexes of palatalizations. It then goes on to discuss the variation before the split of the common Slavic community into three branches. This is followed by the presentation of early East Slavic tribal dialects. Next, early lexical differences across and within Slavic languages are considered. The discussion continues by addressing inter-Slavic areal features and prosodic continua. Finally, external factors of fragmentation are discussed (economic, political), alongisde contacts with non-Slavic languages and sociolinguistic factors.