The U.S. Patent and Trademark Office has announced a new registration category just for nanotechnology inventions.

The patent office’s definition requires that a least one dimension of an invention be less than 100 nanometers and the nanoscale element of the product or process must be essential to whatever properties make it novel.

The patent office began training its examiners in nanotechnology concepts and terminology in November, and has set up a working group of outside lawyers and researchers to give advice. But that has not been enough to head off confusion; a number of overlapping patents have already been issued.