In Taiwan, the determination of patent validity is a dual-track system. According to the Intellectual Property Case Adjudication Act, the IP Court will independently rule on patent validity issues in IP-related civil procedures. On the other hand, an alleged infringing party can file an invalidation action with the IP Office to challenge the validity of the patent in accordance with the Patent Law. When the validity of a patent is determined differently in final conclusive civil and administrative decisions, how the issues would be dealt with has thus received much attention. In this regard, in a recent rehearing case relating to a civil patent infringement litigation, the IP Court and the Supreme Court came to different opinions.