The tagset of the National Corpus of Polish (Polish: Narodowy Korpus Języka Polskiego, hence the acronym NKJP; http://nkjp.pl/), henceforth the NKJP Tagset, is a positional morphosyntactic tagset of Polish. There are 36 grammatical classes (roughly, parts of speech, e.g., adjective). For each grammatical class there is a list of obligatory and optional grammatical categories (e.g., case and number), with the total of 13 different categories in Polish. Each grammatical category has an associated list of possible values (e.g., singular and plural for the grammatical number). In this definition of the NKJP Tagset, all grammatical classes are complex/open Data Categories (DCs), grammatical categories are complex/closed DCs, and the values of grammatical categories are simple DCs.