Both Baltic languages, which are still alive, have preserved their historical territorial dialects. The article gives a brief insight into the research of Latvian and Lithuanian dialects, which are the continuation of ancient languages of Baltic tribes, perhaps with many changes and mutual influence. Only the Livonian dialect of Northern Kurzeme has to be mentioned as an exception because of the Livonian language and the Couronian tribe language as the basis of it. Subdialects, as the smallest territorial units of language in Latvia and Lithuania (points) had formed themselves during feudalism, when peasants did not have the right to change their place of residence. The first recordings of the peculiarities of Latvian and Lithuanian dialects have been known since the 17th-century dictionaries and grammars. The systematic classification of both Latvian and Lithuanian dialects began in the second half of the 19th century. In Latvia, the first who described all three Latvian dialects in his Lettische Grammatik was Gotthard Friedrich Stender. In Lithuania, both Lithuanian dialects were distinguished by August Schleicher.
The first research in Latvian and Lithuanian dialectology and geolinguistics dates back to the second half of the 19th century. The first map of Lithuanian dialects was published by Friedrich Kurschat in 1876. The first geolinguistic maps of the Latvian language were developed by August Bielenstein. They were published in 1881 and 1892. The early programmes of collecting the cultural and linguistic heritage of the Lithuanian and Latvian folklore and language were published at the end of the 19th century. They are very different.
The boundaries of the territorial dialects of Latvian, unlike the Lithuanian, are not determined by one or two dialectal features, but by a set of isoglosses, reflecting phonetic and morphological features. In Lithuanian dialectology, the system of settlements (points) was chosen – language material was collected within approx. 10–12 km radius around them.
In the 1950s, geolinguistic research in Lithuania and Latvia are connected with the creation of national dialectal atlases. In 1977, for the first time in the history of Baltic geolinguistics, the material of Lithuanian and Latvian dialects was collected according to a united program for the Atlas linguarum Europae. In it, Latvian was represented with 36 subdialects and Lithuanian with 42 subdialects. At the beginning of the 21st century, Latvian and Lithuanian linguists have launched a joint project, the Atlas of the Baltic Languages.
We can draw the conclusion that the research of dialects in Latvia and Lithuania for more than a century have been parallel but different, dialectal material was collected according to different programmes.