This article discusses the use of istiṣlāḥi reasoning to answer the contemporary problem such as the MPU's Decree (Majelis Permusyawaratan Ulama) in Aceh on immunization.The reasoning of Islamic law often used to answer contemporary problems is the istiṣlāḥi reasoning. Although thei stiṣlāḥiy reasoning is more flexible in explaining the law of contemporary issues, but in the proc…