Doctor rerum naturalium (Dr. rer. nat.), literally: Doctor of the things of nature, doctor of natural sciences, is a post-graduate academic degree awarded by universities in some European countries (for instance in Germany and Austria) to graduates in mathematics, physics, chemistry, biology, geology, computer science, other natural sciences, and similar areas. These doctoral degrees are equivalent to a PhD. German universities often translate a Dr. rer. nat. to doctorate of science.
Even when a "PhD" and a Dr. rer. nat. are equivalent, they are not interchangeable, as a matter of German law.
In the Czech Republic and Slovak Republic (former Czechoslovakia), a similar designated degree, abbreviated RNDr., is awarded, but should not be confused with Dr. rer. nat., as the former is only an extension of a master-like degree.