The Blue Danube is the New Year's Eve song traditionally associated with the Vienna Philharmonic New Year's Concert.
The work's full title is An der schönen blauen Donau, usually translated as The Blue Danube. Johann Strauss II composed it in 1866, and it became one of the best-known pieces connected with Vienna. At the concert, the audience traditionally applauds when the opening melody is recognized, even though the work is not always performed at exactly the same point in the program.
The concert itself is held on New Year's Day rather than New Year's Eve, but its broadcast is closely tied to the holiday period. It features music by the Strauss family and other composers, performed in Vienna's Musikverein. The program is repeated in several performances because demand for tickets is exceptionally high.
The concert's traditional finale is the Radetzky March, not The Blue Danube. That distinction is a common source of confusion when the two pieces are discussed together.