Walter Kollo (28 January 1878 – 30 September 1940) was a German composer of operettas, Possen mit Gesang, and Singspiele as well as popular songs. He was also a conductor and a music publisher.

Kollo was born in Neidenburg, East Prussia. His best known work, the operetta Wie einst im Mai (1913), was the basis of a 1917 Sigmund Romberg operetta in America entitled Maytime. Kollo died in Berlin.

A merchant's son, he was originally supposed to take his father's trade, but was able to devote himself to the study of music in the Königsberg Sondershausen music conservatory with his mother's help. He became a theater conductor for a brief time in Königsberg before going to Berlin in 1899. In Berlin, he turned towards popular / light music, and from 1908, wrote music for the popular musical theater. It was in 1910 with Willy Bredschneider that he composed his first great success, Große Rosinen, produced on New Year's Eve 1911. Somewhat prolifically, he continued composing musical comedies, farces and operettas, notably, with among other pieces, Wie einst im Mai (1913; with the songs Es war in Schöneberg im Monat Mai and Die Männer sind alle Verbrecher), Der Juxbaron (1916), Drei alte Schachteln (1917) and Die Frau ohne Kuß (1924).

Kollo also emerged as a composer of revues and sound films in 1915, was one of the founders of the performer's rights organization GEMA, and had his own music publishing company. Later he made successful concert tours as a conductor of his own works.

With Jean Gilbert and Paul Lincke, Kollo was a founder of the Berliner Operette.

His son Willi Kollo was also a composer of light music and his grandson is the celebrated Wagnerian tenor René Kollo.