24 Frontiers in Law, 2023, 2, 24-29 E-ISSN: 2817-2302/23 The Role of Islamic Law in Enriching the Decisions of the Indonesian Constitutional Court Zaka Firma Aditya * , Abdul Basid Fuadi and Rizkisyabana Yulistyaputri Expert Assistant to Justice, the Center for Research and Case Analysis, The Constitutional Court of The Republic of Indonesia, Jakarta, Indonesia Abstract: This article discusses the role of Islamic Law in enriching legal considerations of constitutional court decisions. As one of the recognized laws in Indonesia, it turns out that Islamic Law has an essential role in the development of national law, including the Constitutional Court decision. It was proven by the existence of 20 decisions by the Constitutional Court on judicial review of laws with Islamic Law. However, of the 20 decisions, there were only six decisions in which the Constitutional Court used Islamic Law as the basis for its consideration. In this article, we will discuss several things, namely the construction of Islamic Law and the development of positive law in Indonesia. Meanwhile, the penultimate part argues that efforts to legal positivism in Indonesia have been going on for a long time. Before conclusion, the last part believes that in fact, there are nuances of Islamic theory or Islamic Law used by the Constitutional Court judges in several decisions of the Constitutional Court. Keywords: Islamic law, constitutional court, decision, nuances. 1. INTRODUCTION Adhere to law, Indonesia adheres to three legal systems at the same time that lives and develops in society, namely the civil law system (Dutch colonial heritage), the adat law system, and the Islamic law system. The three legal systems complement each other independently [1]. Islamic Law affects the style of Indonesian Law due to the majority of the population in Indonesia adheres to the religion of Islam (87.2 % of the total population of around 268 million people) [2] which allows Islamic Law to become an essential and influential part of the legal system in Indonesia. Islamic Law is also a source of national law development [3]. The three legal systems also eclectically colour the laws issued by the State from the level of legislation to the level of technical regulations [4]. The enforcement of Islamic law as a source of national law development was in accordance with Pancasila, especially the first precepts, namely "God Almighty" and Article 29 of the 1945 Constitution. Article 29 of the 1945 Constitution above is the basis of legitimacy for the positivization of laws derived from Islamic law into national law through the legislative process. Islamic law influences Indonesian legislation because many laws have Islamic legal nuances. For example, Law Number 1 of 1974 concerning Marriage, Law Number 7 of 1989 concerning the Religious Courts, Law Number 23 of 2011 concerning Management of Zakat, Law Number 41 of 2004 concerning Waqf, Law Number 19 of 2008 *Address correspondence to this author at the Expert Assistant to Justice, the Center for Research and Case Analysis, The Constitutional Court of The Republic of Indonesia, Jakarta, Indonesia; E-mail: zaka.firma@mkri.id concerning State Sharia Securities, Law Number 21 of 2008 concerning Sharia Banking, and Law Number 33 of 2014 concerning Guarantee of Halal Products. In practice, justice seekers not only resolve various legal problems through the judiciary under the Supreme Court, but also through the Constitutional Court by taking judicial review because they think that a provision in the Law is contrary to the 1945 Constitution. Then, based on the recapitulation of judicial review at the Constitutional Court, until the end of 2020, there were at least 20 decisions regarding the judicial review of laws that were of Islamic law. This fact shows that the Court has a role in determining the dynamics of the development of Islamic law in Indonesia. Besides that, it also plays a role in enriching the legal considerations of constitutional judges in deciding cases that have Islamic legal material. Because, when there is such a case, it is obligatory for Constitutional Court Judges to use an Islamic legal approach in resolving the case. 1.2. Research Method and Benefit This paper is the result of normative legal research. There are two legal approaches used in this research, namely the statutory approach, namely by examining laws with Islamic legal nuances; and the case approach by examining judicial review decisions against laws containing Islamic law. This reserach aims to analyze the constitutional court decisions which contain Islamic law in its legal considerations. 1.3. Paper Structure This article will discuss how the role of Islamic law ensuring that the legal reasoning of the Constitutional