古斯塔夫·马勒（德语：Gustav Mahler，德语发音：[ˈɡʊstaf ˈmaːlɐ]，1860年7月7日－1911年5月18日），奥地利作曲家、指挥家。作为作曲家，他是19世纪德奥传统和20世纪早期的现代主义音乐之间承前启后的桥梁。马勒之后，十二音和无调性音乐等先锋理念崛起，传统调性音乐的辉煌时代走向终结。他的指挥成就在生前就已得到广泛认可，但他所创作的音乐一度被忽视，在纳粹德国时期甚至因其犹太身份而被禁止，直至第二次世界大战后才因指挥家伯恩斯坦等人的推广而得到复兴，其音乐价值方为人所周知。到如今，马勒的音乐是演出和录音最频繁的作品。

Gustav Mahler (7 July 1860 – 18 May 1911) was an Austrian late-Romantic composer, and one of the leading conductors of his generation. As a composer he acted as a bridge between the 19th century Austro-German tradition and the modernism of the early 20th century. While in his lifetime his status as a conductor was established beyond question, his own music gained wide popularity only after periods of relative neglect which included a ban on its performance in much of Europe during the Nazi era. After 1945 his compositions were rediscovered and championed by a new generation of listeners; Mahler then became one of the most frequently performed and recorded of all composers, a position he has sustained into the 21st century.