The Lusatian Neisse (Czech: Lužická Nisa; German: Lausitzer Neiße; Polish: Nysa Łużycka; Sorbian: Łužiska Nysa) is a river in the Czech Republic (54 km) and along the Polish-German border (198 km), in total 252 km long. It is a left tributary of the Oder River, into which it flows near Gubin. It originates in the Jizera Mountains near Nová Ves nad Nisou.

Since the river runs through the historic region of Lusatia, the adjective before the name of the river Neisse (English: Lusatian; Czech: Lužická; German: Lausitzer; Polish: Łużycka; Sorbian: Łužiska) differentiates this particular river in each language. In 1945 it became the Polish western border to Germany as a result of World War II (see Oder-Neisse line). It thus became the most notable of the three rivers called Neiße (German) or Nysa (Polish), and therefore is often simply called Neisse.