Friedrich Wolfgang Adler (July 9, 1879 – January 2, 1960) was an Austrian socialist politician and revolutionary. He is perhaps best known for his assassination of Count Karl von Stürgkh in 1916.

Adler was born in Vienna, the son of social democratic politician, Victor Adler, and the writer, Emma Adler. He studied chemistry, physics and mathematics in Zurich. In 1897, he became a member of the Social Democratic Party of Austria (SPÖ) and from 1907 was editor of the magazine Der Kampf. He was an acquaintance of Albert Einstein.

He participated in the philosophical discussion about Ernst Mach, publishing Die Entdeckung der Weltelemente (zu E. Machs 70. Geburtstag) - The Discovery of the World-Elements (On the Occasion of E. Mach's 70th Birthday) published in Der Kampf in 1908. This was hostilely cited by Vladimir Lenin in Materialism and Empirio-criticism, who called Adler a "naïve university lecturer". This was part of Lenon's attack on the Russian Machists.

In 1909-1910, while established in the University of Zurich, Adler was being considered to chair the physics department, but deferred to Einstein's superior expertise and lobbied for Einstein's appointment instead.

In 1910, Adler became editor of the newspaper Volksrecht in Zurich. He was engaged in the international trade union movement and in 1911 he gave up his scientific activities to become the secretary-general of the SPÖ in Vienna, an office he held until 1914. He became the spokesperson of the left wing of the party and after the start of the First World War he agitated particularly against the SPÖ's policy of supporting the war.

In his fight against the war policy of Austria-Hungary, Adler resorted to drastic measures. On October 21, 1916, in the dining room of the Viennese hotel Meißl und Schadn, he shot the Minister-President of Austria Count Karl von Stürgkh three times with a pistol, killing him. After a period when attempts were made to avoid a trial by declaring Adler insane, he went to trial in May 1917 where he was able to publicly present his act in the context of the case against the war. Adler was sentenced to death, a sentence which was commuted to 18 years imprisonment.

After the outbreak of the revolution of 1918, he was released and played a significant role as the leader of the Arbeiterräte (workers' councils) and as a member of the National Council of Austria. Adler was secretary of the International Working Union of Socialist Parties in 1921, and subsequently active in the formation of the Labour and Socialist International, serving as secretary-general firstly jointly with Tom Shaw then on his own until 1940.

After the outbreak of the Second World War, Adler fled to the United States. In 1946, he retired from politics and edited his father Victor's exchange of letters with August Bebel and Karl Kautsky.

Adler died on January 2, 1960 in Zurich.