Hermann August Hagen (30 May 1817 – 9 November 1893) was a German entomologist who specialised in Neuroptera and Odonata.

He had established himself as one of Europe's preeminent entomologists by 1867 when he accepted a position at Harvard University to curate the Museum of Comparative Zoology.

His course of studies was greatly influenced by his zoology professor, Martin Heinrich Rathke and together they toured major entomological collections and libraries in Norway, Sweden, Denmark and Germany.

In 1843, he returned to Königsberg, entered into the general practice of medicine, and for three years was first assistant at a surgical hospital.

He published several papers on dragonflies as a result of his close collaboration with Edmond de Sélys Longchamps.

[1] In spite of a busy medical practice and a full program of scientific studies, Hagen also found time to serve as a member of the school board and vice-president of the city council in Königsberg from 1863 to 1867.

While holding these civic offices, he was invited by Louis Agassiz to come to Cambridge as assistant in entomology at the Museum of Comparative Zoology at Harvard.

However, in 1882 he participated in a survey of insect pests along the Northern Pacific Railroad, traveling through Montana, California, Oregon and Washington.