"Naturphilosophie" (German for "nature-philosophy") is a term used in English-language philosophy to identify a current in the philosophical tradition of German idealism, as applied to the study of nature in the earlier 19th century. German speakers use the clearer term "Romantische Naturphilosophie", the philosophy of nature developed at the time of the founding of German Romanticism. It is particularly associated with the philosophical work of Friedrich Wilhelm Joseph Schelling and Georg Wilhelm Friedrich Hegel—though it has some clear precursors also. More particularly it is identified with some of the initial works of Schelling during the period 1797–9, in reaction to the views of Johann Gottlieb Fichte, and subsequent developments from Schelling's position. Always controversial, some of Schelling's ideas in this direction are still considered of philosophical interest, even if the subsequent development of experimental natural science had a destructive impact on the credibility of the theories of his followers in Naturphilosophie.

Naturphilosophie attempted to comprehend nature in its totality and to outline its general theoretical structure, thus attempting to lay the foundations for the natural sciences. In developing their theories, the German Naturphilosophen found their inspiration in the natural philosophy of the Ancient Greek Ionian philosophers.

As an approach to philosophy and science, Naturphilosophie has had a difficult reception. In Germany, neo-Kantians came to distrust its developments as speculative and overly metaphysical. For most of the 19th and early 20th centuries, it was poorly understood in Anglophone countries. Over the years, it has been subjected to continuing criticism. Since the 1960s, improved translations have appeared, and scholars have developed a better appreciation of the objectives of Naturphilosophie.

The German idealist philosopher Johann Gottlieb Fichte had attempted to show that the whole structure of reality follows necessarily from the fact of self-consciousness. Schelling took Fichte's position as his starting-point, and in his earliest writings posited that nature must have reality for itself. In this light Fichte's doctrines appeared incomplete. On the one hand, they identified the ultimate ground of the universe of reason too closely with finite, individual Spirit. On the other, they threatened the reality of the world of nature by seeing it too much in the manner of subjective idealism. Fichte, in this view, had not managed to unite his system with the aesthetical and teleological view of nature to which Immanuel Kant's Critique of Judgment had pointed.

Naturphilosophie is therefore one possible theory of the unity of nature. Nature as the sum of what is objective, and intelligence as the complex of all the activities making up self-consciousness, appear as equally real. The philosophy of nature and transcendental idealism would be the two complementary portions making up philosophy as a whole.

Naturphilosophie translated into English would mean "philosophy of nature", and its scope began to be taken in a broad way. Johann Gottfried Herder, particularly taken in opposition to Immanuel Kant, was a precursor of Schelling:

Herder's dynamic view of nature was developed by Goethe and Schelling and led to the tradition of Naturphilosophie [...]

Later Friedrich Schlegel theorised about a particular German strand in philosophy of nature, citing Jakob Böhme, Johannes Kepler and Georg Ernst Stahl, with Jan Baptist van Helmont as an edge case. Frederick Beiser instead traces Naturphilosophie as developed by Schelling, Hegel, Schlegel and Novalis to a crux in the theory of matter, and identifies the origins of the line they took with the vis viva theory of matter in the work of Gottfried Leibniz.