2019年通過的憲法訴訟法，參考美國法制，於第20條第1項引入「法庭之友（Amicus Curiae）」制度。本文將以此一新制度的功能、實效與憲法法庭審理規則中應有的細部配套設計為主要探討對象。同時，有鑑於憲法訴訟法兼採美國法庭之友與德國專家意見陳述（鑑定制度）兩項制度，究竟二者有何異同，未來實務上又應如何選擇、操作，本文也將嘗試提出觀察與建議。第貳部分將先介紹美國聯邦最高法院法庭之友制度，此一制度不但有著「民主增強」的功能，也提供了法院決定是否受理案件的重要信號，並豐富了案件實體爭點的意見，對於釐清爭議、充分掌握判決的影響，有相當的功效。此部分並進一步剖析美國法庭之友的各項細部規範，以做為我國的參考。接著於第參部分，回歸憲法訴訟法的規定，對我國未來審理規則內容，包括法庭之友的主體資格、聲請程序與要件等事項，提出具體建議。第肆部分，則針對法庭之友與專家意見陳述（鑑定）制度進行比較分析；本文認為，未來在憲法法庭的審理實務上，短期或許仍將依賴行之有年的鑑定制度，但若法庭之友制度可以有效運作，應該成為憲法法庭獲取外部意見的主要管道。最後於本文第伍部分，將綜合前述觀察作成結論。

The Constitutional Court Procedure Act (CCPA) was enacted in 2019. The Act, by reference to the U.S. law, adopts the amicus curiae system. This article will mainly focus on the functions and potential contributions of the new system, and discuss corresponding regulations that should be included in the Rules of the Constitutional Court. Meanwhile, as the CCPA also retains the existing expert witness system, this article will compare the two systems and make suggestions on how the Court should choose and implement these tools. Part two of the article will first explore the U.S. Supreme Court’s amicus curiae system. This article finds that amicus curiae not only has the “democracy-enhancing” function, but also serves as an important signal of whether the Supreme Court should grant certiorari to a case. In addition, amicus curiae may provide valuable opinions on the issues of the case, and assist the Court to better solve the dispute and grasp the potential impact of its decision. This part will then discuss in details the Rules of the Supreme Court concerning amicus curiae. In part three, this article will focus on the CCPA, and make concrete suggestions on how the Rules of the Constitutional Court should regulate amicus curiae regarding its qualifications, the application procedure, and related matters. Part four of the article will compare amicus curiae with expert witness. This article believes that in the short term, the Constitutional Court will need to rely on the longstanding expert witness system; however, if amicus curiae can properly function, it should become the major source for the Court to obtain outside opinions in the future. Lastly, in Part five, the article will conclude that the incorporation and implementation of amicus curiae will start a new chapter of the already successful constitutional review system in Taiwan.