German mathematician who made important contributions to number theory.

Eisenstein's family converted to Protestantism from Judaism just before his birth. He was the oldest of six children and the only one of them to survive childhood meningitis. Eisenstein entered the Friedrich Wilhelm University (now the Humboldt University of Berlin) in 1843 and the following year published 25 papers in August Leopold Crelle (Crelle, August Leopold)'s prestigious mathematical journal. Crelle introduced him to the naturalist Alexander von Humboldt (Humboldt, Alexander von), who became his lifelong mentor and sponsor. Humboldt in turn encouraged an exchange of correspondence with mathematician and physicist Carl Friedrich Gauss (Gauss, Carl Friedrich), who wrote a preface to the first edition of Eisenstein's Mathematische Abhandlungen (1847; “Mathematical Treatises”). Eisenstein became a professor of mathematics at Berlin in 1847 and was elected to the Royal Prussian Academy of Sciences and Humanities (now the Berlin-Brandenburg Academy of Sciences and Humanities) shortly before his death.

In 1975 his mathematical work, in two volumes, was published as Mathematische Werke.