Volume I of Mueller on Patent Law covers patentability and validity. It offers a clear-cut approach to understanding the multiple, rigorous requirements for obtaining a U.S. patent. Following introductory chapters overviewing the patent system and the central importance of patent claims, Volume I explicates the cornerstone requirement of novelty and what counts as prior art under both pre- and post-AIA regimes. Volume I also tackles the amorphous landscape of patent eligibility, as well as the bedrock requirements that a patentable invention be useful and not only new but nonobvious. Separate chapters unpack the patent application disclosure requirements of enablement, written description, and best mode. Volume I concludes with chapters analyzing inventorship, the prohibition on double patenting, and the nuts and bolts of prosecuting patents in the USPTO.