The aim of the article is to collect and present studies into text comprehensibility conducted so far. The author examines studies dealing with plain language, Polish language teaching and pedagogy. The article opens with an overview of the history of research into text difficulty in the world featuring various concepts of automatic measurement of text difficulty level. Next the author presents studies devoted to comprehensibility of utterances in Poland, as well as studies concerning text difficulty with regard to language teaching. This is followed by a discussion of the principles of the text simplification principle according to the Wrocław plain language model and in the teaching of Polish.
The article closes with a short overview of publications containing simplified authentic texts used in the teaching of Polish as a foreign language.