Several articles reported that Nikola Tesla owned 700 patents (one article states he had 600 to 700 patents).

According to a recent study by the IEEE, an organization that Tesla once belonged to:

Newly Discovered Tesla Patents: This paper presents the results of a continuation of the investigation aiming to discover and identify the previously unknown Nikola Tesla's patents. The investigation shows that Nikola Tesla had at least 308 patents originating from 27 countries. Though the newly discovered patents are members of the previously defined patent families, they give a new insight into his activities on protecting the inventions internationally, especially at the beginning. The subject matter of 28 newly discovered patents from 7 countries is different Tesla's inventions in electrical and mechanical engineering.

It is possible that Nikola Tesla exaggerated his number of patents, although this seems unlikely given his character. More likely is that Tesla did file nearly 700 patents, and considering their importance to the military, the patents were classified and removed from public view. Also, considering all the claims Tesla had made for his unusual technologies, many of these technologies which later appeared in the arsenal of the US and foreign militaries, it is likely that nearly 400 of his patents are still hidden from public view.