Ernst, Count of Lippe-Biesterfeld (Ernst Kasimir Friedrich Karl Eberhard; 9 June 1842 – 26 September 1904) was the head of the Lippe-Biesterfeld line of the House of Lippe. From 1897 until his death he was the regent of the Principality of Lippe.

He was born in Oberkassel the third child of Julius, Count of Lippe-Biesterfeld (1812–1884) and Countess Adelheid of Castell-Castell (1818–1900). On 17 May 1884 Count Ernst succeeded his father as the head of Lippe-Biesterfeld line of the House of Lippe. After the reigning Princes of Lippe, Biesterfeld was the most senior line of the princely house followed by the counts of Lippe-Weissenfeld and the princes of Schaumburg-Lippe.

On 20 March 1895 the reigning prince of Lippe, Prince Woldemar died childless. His heir was his brother Alexander who was incapable of ruling on account of a mental illness so a regency had to be established. A decree had been issued in 1890 by the late Prince Woldemar and though kept secret until his death it resulted in Prince Adolf of Schaumburg-Lippe, the brother in law of the German Emperor William II and not Count Ernst being appointed regent.

This act was disputed by Count Ernst who put forward a claim to the regency. Lippe's diet confirmed Prince Adolf as regent on 24 April pending a settlement over the right to the Lippe regency.

In the first scene (1895–97) of the Lippe succession dispute, it was claimed on part of the Schaumburg-Lippe that count Ernest's paternal grandmother, noblewoman Modeste von Unruh (who belonged to a family of lower nobility) was not noble enough to be legitimately a dynastic wife - that would have made progeny born of her ineligible to succeed.

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