备忘意见书（英语：Memorandum opinion，或英语：Memorandum decision），法律术语，源自英美习惯法，是法律意见书的一种。一般来说，它的内容通常比较简短，主要的用途是为了在特殊案例中，让法官作为宣判前的准备之用。因此，备忘意见书不会成为判决先例、具备说服力的先例（Persuasive precedent）、或具备拘束力的先例（Binding precedent）。

Under United States legal practice, a memorandum opinion is usually unpublished and cannot be cited as precedent. It's formally defined as: "[a] unanimous appellate opinion that succinctly states the decision of the court; an opinion that briefly reports the court's conclusion, usu. without elaboration because the decision follows a well-established legal principle or does not relate to any point of law."