Henrik Steffens (2 May 1773 – 13 February 1845), was a Norwegian born Danish philosopher, scientist, and poet.

He was born at Stavanger, Norway. At the age of fourteen he went with his parents to Copenhagen, where he studied theology and natural science. In 1796 he lectured at the University of Kiel, and a year later went to the University of Jena to study the natural philosophy of Friedrich Schelling. He went to Freiburg in 1800, and there came under the influence of Friedrich Werner.

After two years he returned to Copenhagen, and is said to have introduced German romanticism to Denmark in 1802 with nine lectures given at Elers Kollegium, later published as Indledning til philosophiske Forelæsninger (Introduction to Philosophical Lectures). These lectures were a great success and a source of inspiration in Danish romanticism. They were attended by many who would later become leading Danish thinkers, such as Oehlenschläger and Grundtvig. Friedrich Schleiermacher was so much struck by their excellence that he endeavoured, unsuccessfully, to obtain for Steffens a chair in the new Berlin University in 1804, in order that his own ethical teachings should be supported in the scientific department.

Despite – or perhaps because of – the deep impact made by his lectures, Steffens was not made welcome by the Danish authorities. He moved back to Germany and took up a professorship at the University of Halle in 1804, to return to Denmark only occasionally. During the Battle of Leipzig (1813) he enlisted in the Prussian Army as a second lieutenant, and he was present at the capture of Paris the following year. He was professor of physics at Breslau from 1811 until 1832, when he accepted an invitation to Berlin.

Steffens was one of the so-called "Philosophers of Nature", a friend and adherent of Schelling and of Schleiermacher. More than either of these two thinkers he was acquainted with the discoveries of modern science, and was thus able to correct or modify the highly imaginative speculations of Schelling. He held that, throughout the scheme of nature and intellectual life, the main principle is Individualisation. As organisms rise higher in the scale of development, the sharper and more distinct become their outlines, the more definite their individualities. This principle he endeavoured to deduce from his knowledge of geology, in contrast to Lorenz Oken, who developed the same theory on biological grounds. His influence was considerable, and both Schelling and Schleiermacher modified their theories in deference to his scientific deductions.

During the last five years of his life he wrote an autobiography, Was ich erlebte, and after his death his Nachgelassene Schriften (1846) was published.