[Sean B. Seymore] Abstract: A bedrock principle of patent law is that old inventions cannot be patented. And a new use for an old invention does not render the old invention patentable. This is because patent law requires novelty—an invention must be new. But while a new use for an old invention does not make the old invention patentable, a new use for an old invention might be patentable. In fact, new-use patents comprise a significant part of the patent landscape—particularly in pharmaceuticals as drug companies obtain new-use patents to repurpose old drugs. This trend has fueled debates over follow-on innovation and patent quality. But there is a problem with new-use patents that has escaped the attention of legal scholars and commentators.