ABSTRAK: Sebagai cabang dari hukum kontrak, kontrak penanaman modal internasional pada umumnya diatur dalam hukum privat. Meskipun demikian, berbeda dengan kontrak dan kontrak internasional pada umumnya yang diatur sepenuhnya dalam hukum privat, kontrak penanaman modal internasional juga diatur dalam hukum publik. Prinsip dan kaidah hukum kontrak penanaman modal internasional dapat ditemukan baik dalam hukum administrasi/tata negara, maupun dalam hukum internasional publik. Hukum publik tersebut, antara lain, mengatur kewenangan subjek terkait kapasitas kontrak, prosedur perancangan, isi minimum, pilihan memaksa terhadap hukum domestik, arbitrase internasional, dan klausula payung dalam traktat penanaman modal internasional. Kenyataan demikian menunjukkan pentingnya pendekatan sistem dalam pemahaman, penerapan, dan pembaruan hukum tersebut secara menyeluruh. System Approach Toward Public Law in International Investment Contracts ABSTRACT: As a branch of contract law, international investment contracts are generally regulated under private law. However, different from contracts and international contracts in general which are regulated under private law, They are also regulated under public law. The public law principles and norms of international investment contracts can be found in administrative/costitutional law, and in public international law. The public law regulate, among others, authority of subject related to capacity to contracts, drafting procedure, minimum contents, mandatory choice of domestic laws, international arbitration, and umbrella clause in bilateral investment treaties (BITs). This fact indicates the importance of system approach for total understanding, application, and reform of the law.