Landgravine Louise Auguste of Hesse-Darmstadt (30 January 1757 – 14 February 1830) was a German princess. She was the daughter of Louis IX, Landgrave of Hesse-Darmstadt. On 3 October 1775 she married duke (later grand-duke) Charles Augustus of Saxe-Weimar-Eisenach and as such a member of the court sphere of Weimar Classicism. She was held to be serious and introverted but also compassionate and sympathetic, in the aftermath of the Battle of Jena which guaranteed her part in the later "myth of Weimar" ("Weimarmythos").

The princess belonged to the House of Darmstadt, which held the Hessian landgraviate. She was born on 30 January 1757 in Frederick II's Prussian capital, Berlin, where her parents were due to the Seven Years' War. Her father Louis IX succeeded to the landgraviate in 1768 and was at the time of her birth fighting as a general for the Prussian forces. He was thus often away from his children and so the princess's education was in her mother Caroline's hands. Caroline educated Louise in the evangelical Protestant tradition, and she became interested in literature and music.

As the youngest daughter, with eight siblings, Louise's education was important to improve her marriage prospects. Since Louis IX showed little interest in his children, it was vital to get Louise married off and a matter also in the hands of her mother, becoming known as the "great Landgräfin" and von Zweibrücken due to her expert international dynastic politics in ancien regime Europe. In 1773 Louise travelled with her mother and sisters Amalie and Wilhelmine to Beschau then to the Russian court in St Petersburg. Tsarina Catharine II decided Louise was unsuitable as a wife for the grand-prince and future Tsar Paul, preferring her sister Wilhemine. This rebuff and her relationship with her future brother-in-law Paul formed Louise, leading to her being a persistent influence in the Russian state.

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