In the field of old literary language, the corpus of old literary Estonian is compiled, consisting of material from as early as the 13th century, varying from the Estonian sentences found on Livonian Chronicle of Henry, to fiction written by Estonian authors in the late 19th century. Original software has been developed that is used to compile and annotate the corpus. The corpus is used to study phonological, morphological, morphosyntactic and pragmatic phenomena in old literary Estonian. The focus of the research is the development of vocabulary reflected in the old literary language. Diachronic grammar studies deal with language variation and change, including grammaticalization and pragmatization. Among the phenomena, the focus of interest has been the development of conjunctions and infinitive constructions as well as the use of particles, including the development of interrogative particles.
In the framework of historical sociolinguistics, the use of the Estonian literary language has been discussed in different periods, e.g. the stage of the German-influenced Estonian language and the 19th century fusion language.
Research has focused on the Northern Estonian language, there are fewer approaches to the Southern Estonian language. Of the languages that developed in a similar historical situation, the data of the Finnish language, but also Latvian, Livonian and Sorbian are taken into account.
Source publications, voluminous dictionaries and scholarly articles have been published based on the corpus studies.