The grammar of the Polish language is complex and characterized by a high degree of inflection, and has relatively free word order, although the dominant arrangement is subject–verb–object (SVO). Polish lacks articles (although this has been a subject of academic debate), and there is frequent dropping of subject pronouns. Distinctive features include the different treatment of masculine personal nouns in the plural, and the complex grammar of numerals and quantifiers.

Certain regular or common alternations apply across the Polish inflectional system, affecting the morphology of nouns, adjectives, verbs, and other parts of speech. Some of these result from the restricted distribution of the vowels i and y, and from the voicing rules for consonants in clusters and at the end of words. Otherwise, the main changes are the following:

Polish retains the Old Slavic system of cases for nouns, pronouns, and adjectives. There are seven cases: nominative (mianownik), genitive (dopełniacz), dative (celownik), accusative (biernik), instrumental (narzędnik), locative (miejscownik), and vocative (wołacz).

Polish has two number classes: singular and plural.

It used to also have the dual number, but it vanished around the 15th century. It survived only in a few relicts:

For true nouns (not for adjectives), there are three cases that always have the same ending in the plural, regardless of gender or declension class: dative plural in -om, instrumental plural in -ami or -mi, and locative plural in -ach; the only apparent exception being nouns that are in fact inflected as previously dual nouns, ex. rękoma instrumental plural of ręka "hand".

There are three main genders (rodzaje): masculine (męski), feminine (żeński) and neuter (nijaki). Masculine nouns are further divided into personal (męskoosobowy), animate (męskożywotny), and inanimate (męskorzeczowy) categories. Personal and animate nouns are distinguished from inanimate nouns in the accusative singular; for the latter the accusative is identical to the nominative. In the plural, the masculine personal nouns are distinguished from all others, which collapse into one non-masculine personal gender (niemęskoosobowy).

The following tables show this distinction using as examples the nouns mężczyzna 'man' (masc. personal), pies 'dog' (masc. animate), stół 'table' (masc. inanimate), kobieta 'woman' (feminine), okno 'window' (neuter). The following table presents examples of how a determiner ten/ta/to ("this") agrees with nouns of different genders in the nominative and the accusative, both singular and plural. Adjectives inflect similarly to this determiner.