Eduard Bernstein (German: [ˈeːduaʁt ˈbɛʁnʃtaɪn]; 6 January 1850 – 18 December 1932) was a German social democratic politician and socialist theorist. A member of the Social Democratic Party (SPD), Bernstein is best known for his reformist challenge to Marxism known as evolutionary socialism or revisionism, in which he questioned the revolutionary predictions of Karl Marx and advocated for a gradual, parliamentary path to socialism. His political and theoretical work played a significant role in the development of modern social democracy and reformist socialism.

Born into a lower-middle-class Jewish family in Berlin, Bernstein became active in socialist politics in his early twenties. He spent years in exile in Switzerland and London during the period of the Anti-Socialist Laws in Germany, where he became a close associate of Friedrich Engels. During his time in London, his interactions with the reformist Fabian Society and his observation of the stability of late Victorian capitalism led him to question key tenets of orthodox Marxism.

After Engels's death in 1895, Bernstein began to publicly articulate his revisionist views. In his most influential work, Evolutionary Socialism (1899), he rejected the Hegelian dialectical method and disputed the Marxist predictions of the inevitable collapse of capitalism, the disappearance of the middle class, and the increasing immiseration of the proletariat. Instead, he argued that socialists should work for gradual social and political reforms through democratic institutions. His famous aphorism, "the goal is nothing, the movement everything," encapsulated his focus on the practical, democratic progress of the socialist movement over a dogmatic adherence to a revolutionary goal.

Although his views were officially condemned by the SPD, which maintained its orthodox Marxist Erfurt Program, the party's practical policies were largely reformist, reflecting the reality Bernstein described. His work sparked major debates within the international socialist movement, pitting him and his supporters against orthodox Marxists like Karl Kautsky and radicals like Rosa Luxemburg. During World War I, Bernstein's pacifist principles led him to break with the SPD's pro-war majority and co-found the anti-war Independent Social Democratic Party (USPD), though he rejoined the SPD after the war. He served in the Reichstag during the Weimar Republic, where he continued to advocate for democracy and peace. He died in Berlin in late 1932, weeks before the Nazi seizure of power.

Eduard Bernstein was born in Schöneberg (now part of Berlin) on 6 January 1850, a time of political reaction in Germany following the failure of the Revolutions of 1848. He was the seventh of fifteen children born to Jakob Bernstein, a railway engine driver, and his wife, Johanne. His family was of Polish-Jewish origin, though they had been secular for two generations; they celebrated Christmas as a German rather than a religious holiday. This environment fostered in Bernstein a skeptical worldview from a young age. The family's income was modest, placing them in the "genteel poverty" of the lower middle class, or petty bourgeoisie. His uncle, Aaron Bernstein, was a prominent liberal journalist and the author of popular science books.

At sixteen, Bernstein left school without finishing Gymnasium due to his family's financial situation and began an apprenticeship at a Berlin bank. He worked as a bank clerk from 1869 until 1878, a profession that provided a livelihood but did not capture his primary interests. His real education was self-directed, and he developed intellectual pursuits in theatre, poetry, and philosophy.

Bernstein's political awakening occurred during the Franco-Prussian War of 1870–1871. Initially a patriot, he became sympathetic to the anti-war stance of socialist leaders August Bebel and Wilhelm Liebknecht after they were accused of treason. In 1872, after reading works by Ferdinand Lassalle and being particularly impressed by a speech from the socialist agitator Friedrich Fritzsche, Bernstein and his friends joined the Social Democratic Workers' Party (SDAP), known as the "Eisenachers" for the town where they were founded. He quickly became a skilled public speaker and an active party member, undertaking grueling speaking tours and engaging in debates with the rival Lassallean socialist party.

The two most influential books on the young Bernstein were Karl Marx's The Civil War in France, an exaltation of the Paris Commune, and Eugen Dühring's Critical History of National Economy and Socialism. His enthusiasm for Dühring's work proved contagious, and he was instrumental in popularizing Dühring's ideas within the socialist movement, even introducing them to Bebel. This early attachment to Dühring's thought, a blend of positivism and idealism, would later be exorcised by Friedrich Engels's sharp critique, Anti-Dühring.