Polish nationalism (Polish: polski nacjonalizm) is a nationalism which asserts that the Polish people are a nation and which affirms the cultural unity of Poles. British historian of Poland Norman Davies defines nationalism as "a doctrine ... to create a nation by arousing people's awareness of their nationality, and to mobilize their feelings into a vehicle for political action."

The nationalism of the Polish–Lithuanian Commonwealth – a polity which existed de facto from 1386, and officially from 1569, until the Commonwealth's 1795 Third Partition – incorporating Poles, Lithuanians, East Slavs, and smaller minorities. was multi-ethnic and multi-confessional, though the Commonwealth's dominant social classes became extensively Polonized and Roman Catholicism was regarded as the dominant religion.

The nationalist ideology which arose soon after the Partitions was initially free of any kind of "ethnic nationalism". It was a Romantic movement which sought the restoration of a Polish sovereign state. Polish Romantic nationalism was described by Maurycy Mochnacki as "the essence of the nation", no longer defined by borders but by ideas, feelings, and thoughts stemming from the past.

The advent of modern Polish nationalism under foreign rule coincided with the November 1830 Uprising and the European Revolutions of 1848 ("the Springtime of Nations"). Their ensuing defeats broke the Polish revolutionary spirit. Many intellectuals turned to Herbert Spencer's social Darwinism and blamed Poland's erstwhile Romantic ("Messianist") philosophy for the insurrectionary disasters.

After the failure of the subsequent Polish January 1863 Uprising, the Romantic schools of thought were firmly displaced by a specifically Polish version of Auguste Comte's Positivist philosophy which dominated Polish thought to the end of the 19th century.

After the three partitioning empires collapsed in World War I, Poland returned as a territorially reduced and ethnically more homogeneous polity – though still with substantial minorities, especially the Ukrainians of southeastern Poland, which themselves began to harbor their own national aspirations.

The earliest manifestations of Polish nationalism, and conscious discussions of what it means to be a citizen of the Polish nation, can be traced back to the 17th or 18th century, with some scholars going as far back as the 13th century, and others to the 16th century. Early Polish nationalism, or protonationalism, was related to the Polish-Lithuanian identity, represented primarily by the Polish nobility (szlachta), and by their cultural values (such as the Golden Freedoms and Sarmatism). It was founded on civic, republican ideas. This early form of Polish nationalism began to fray and transform with the destruction of the Polish state in the partitions of Poland from 1772 to 1795.

Modern Polish nationalism arose as a movement in the late-18th and early-19th centuries amongst Polish activists who promoted a Polish national consciousness while rejecting cultural assimilation into the dominant cultures of Austria, Prussia and Russia, the three empires which partitioned Poland-Lithuania and occupied the various regions of Poland. This was the consequence of Polish statelessness, because the Polish nationality was suppressed by the authorities of the countries which acquired the territory of the former Commonwealth. During that time Polishness begun to be identified with ethnicity, increasingly excluding groups such as the Polish Jews, who had previously been more likely to be accepted as Polish patriots. This was also the period in which Polish nationalism, which was previously common to both left-wing and right-wing political platforms, became more redefined as being limited to the right-wing, with the emergence of the politician Roman Dmowski (1864–1939), who renamed Liga Polska (the Polish League) as Liga Narodowa (the National League) in 1893.