Theodor Fontane was a German novelist and poet, regarded by many as the most important 19th-century German-language realist author. Fontane is known as a writer of realism, not only because he was conscientious about the factual accuracy of details in fictional scenes, but also because he depicted his characters in terms of what they said or did and refrained from overtly imputing motives to them. He published the first of his novels, for which he is best known today, only at age 58 after a career as a journalist. His novels delve into topics that were more or less taboo for discussion in the polite society of Fontane's day, including marital infidelity, class differences, urban vs. rural differences, abandonment of children, and suicide. His novels sold well during his lifetime and several have been adapted for film or audio works. His characters range from lower-middle class to Prussian nobility.

Effi Briest is a realist novel by Theodor Fontane. Published in book form in 1895, Effi Briest marks both a watershed and a climax in the poetic realism of literature. It can be thematically compared to other novels on 19th-century marriage from a female perspective, such as Anna Karenina and Madame Bovary, which are also adultery tragedies.