通常在審查法定適格的專利申請案時，新穎性是除了產業利用性以外，第二個用來被檢驗的要件。雖然實務上，與申請專利範圍不具非顯而易知性被核駁相比，以不具新穎性而被核駁者較少，然而，若是整篇申請案的申請專利範圍都被審查官以不具新穎性而核駁，往往會變得非常難以答辯。所以深入了解美國專利新穎性要件，對專利申請是非常重要的。本文探討在1952年美國專利法以及目前已實施的美國專利改革法案對新穎性要件的定義，並比較分析這兩個新舊專利法對專利新穎性要件的規定。除了針對美國專利法新穎性的探討，本文也針對美國專利改革法案的立法歷程，以及一些重要的規定改變，例如將美國專利制度上的「先發明主義」，變更為「先申請主義」、多方複審程序、領證後複審程序、衍生行政訴訟，做一研究。

For a patent application with a patentable subject matter, novelty is the second requirement for examination after utility requirement.Practically speaking, the rejection under novelty is not as many as that of non-obviousness. However, if all of the claims suffer from rejection under novelty, it will be very difficult to make the argument with the examiner.Therefore, mastering the novelty requirement is crucial to U.S. patent prosecution.The present paper studies the novelty requirements of U.S. patent law of 1952 and the currently-enforced Leahy- Smith America Invents Act (AIA).The present paper also covers comparison and contrast the novelty requirement under AIA and pre-AIA. In addition to the study of novelty requirements under U.S. patent law, the present paper also covers the legislative history and some important changes of AIA.The important changes include changing American patent system from “first to invent” to “first inventor to file”, inter partes review, postgrant review, and derivation proceeding.