The Swedish scientist and inventor Christopher Polhem (1661–1751) had a great and decisive impact on Swedenborg. Traces of Polhem’s ideas can be found in Swedenborgs’s natural philosophy, in his mathemathics, technology, matter theory, and cosmology. Swedenborg was an assistant to Polhem during the years 1716–1719, a period of intense collaboration. Here, I will show how fundamentally Polhem reshaped Swedenborgs thinking. In order to fully understand Swedenborg’s development as a natural philosopher it is necessary to closely investigate his most important mentor.