Alexander Abramovich Krein (Russian: Александр Абрамович Крейн; Aleksandr Abramovich Kreyn; 20 October 1883 in Nizhny Novgorod – 25 April 1951 in Staraya Ruza, Moscow Oblast) was a Soviet composer.
The Krein family was steeped in the klezmer tradition; his father Abram (who moved to Russia from Lithuania in 1870) was a noted violinist. All of the seven Krein brothers received their first musical training from him and became musicians; Alexander and Grigori made names for themselves as composers, David gained a strong reputation as a violinist. Of the three Krein family composers, Alexander, his brother Grigori, and Grigori's son Julian, it is Alexander who composed the most music and thus to whom the most attention has been paid. After decades of posthumous neglect, however, his very name seems to have disappeared from international reference books.
In 1896, at the early age of 14, Alexander Krein entered the Moscow Conservatory where his studies included cello classes with Alexander von Glehn and composition lessons with Sergei Taneyev and Boleslav Yavorsky. His first works were published by P. Jurgenson in 1901. During the years immediately prior to the 1917 Revolution, he was on the faculty of the People's Conservatory in Moscow. In 1917, he was appointed as director of the artistic wing of the Muzo-Narkompros, the music section of a newly formed ministry of arts and aducation. Throughout the 1920s, Krein was widely regarded as the leader of a Jewish national school in Russia (which included his brother Grigori and his nephew Julian). Among those he influenced were minor composers such as Sinovii Feldman. After the formation of the Soviet Union, he held a variety of official and semi-official music administration posts. He died April 1951 in Staraya Ruza. His son, Alexander Kron, was a Soviet playwright.