Związek Ludowo-Narodowy (ZLN; English: Popular National Union) was a Polish political party aligned with the National Democracy political movement during the Second Polish Republic, gathering together right-wing politicians with conservative and nationalist opinions.

Between 1919 and 1926, the Popular National Union achieved considerable electoral success but at no point governed alone. It could only supply individual ministers (e.g. in finance, education or foreign affairs) to successive governments after 1923 in cooperation with the National Democrats and the peasants' party (Chjeno-Piast). In the 1922 presidential elections, the Popular National Union nominated Count Maurycy Zamoyski to counter the centrist Gabriel Narutowicz and the socialist Stanisław Wojciechowski of the Polish People's Party “Piast”.

After the May 1926 Coup, the Popular National Union gradually lost its influence and power in the wake of internal schisms and conflicts under the rule of its rivals, the Sanation regime. In 1928 the Popular National Union morphed into the National Party (Stronnictwo Narodowe).

The ZLN origins as a political party lay in the postwar Europe of late 1918. In December of that year and shortly before the elections, an alliance arose known as the "National Election Committee of Democratic Parties" (Narodowy Komitet Wyborczy Stronnictw Demokratycznych) composed of the following: National Democracy (Narodowa Demokracja); National Unity (Zjednoczenie Narodowe); the Christian Workers' Party (Chrześcijańskie Stronnictwo Robotnicze); and the Polish Progressive Party (Polska Partia Postępowa). During the 1919 elections this alliance obtained 109 seats with most of its representatives hailing from western "Greater Poland)". Wojciech Korfanty became the president of this grouping with Stanisław Grabski, Konstanty Kowalewski and Józef Teodorowicz as vice-presidents. In February 1919 this alliance morphed into the National Parliamentary Popular Union (Związek Sejmowy Ludowo-Narodowy).

The ZLN was established in May 1919 at the 1st Congress of the National Popular Union. At the beginning, the ZLN was a federation of political parties, but the summer of 1919 saw the departure of the Christian-National Workers Club (Chrześcijańsko-Narodowy Klub Robotniczy) from its ranks. This split greatly homogenized the character of the ZLN, a change evident by its second congress conference in October 1919.

In January 1919, a group of National Democrats attempted a coup d’état to bring down the leftist government of Jędrzej Moraczewski. The ZLN's Marian Januszajtis-Żegota and Eustachy Sapieha participated in this unsuccessful attempt.

On 16 January 1919, a non-aligned government arose with the cooperation of ZLN members Władysław Seyda as Minister of the “Prussian” District, Józef Englich in finance, and Reverend Antoni Stychel as Deputy Speaker of Parliament. When the situation at the front of the Polish-Soviet War became critical in spring 1920, the ZLN were prominent in their vocal criticism of Piłsudski and soon inspired the creation of the Council of National Defense (Rada Obrony Państwa) with Roman Dmowski (the de facto intellectual leader of the National Democrats).

At the time, the ZLN's political manifesto could be summarized in a few points: