This document discusses addition and substitution improvement patents. An improvement patent is granted for an enhancement to an existing patented device that is novel and non-obvious. Addition patents involve adding new components, while substitution patents replace major components or materials. When evaluating an improvement patent, its relationship to the original patent must be considered, such as whether it can be practiced without infringing the earlier patent and whether the differences would be obvious. Both patentability and potential infringement are analyzed.