Tesis ini membahas tentang Mekanisme Penetapan Ambang Batas (Threshold) Terhadap Stabilitas Sistem Presidensial dan Sistem Multipartai Sederhana di Indonesia, dengan tujuan untuk mengetahui secara kongkrit syarat-syarat penting terwujudnya pemerintahan presidensial yang efektif, melalui substansi kebijakan penetapan ambang batas yang berlaku di Indonesia, dan implikasi penetapan ambang batas terhadap stabilitas sistem presidensial dan sistem multipartai Indonesia. Penelitian ini dilakukan dengan menggunakan metode penelitian hukum normatif, melalui studi kepustakaan, dengan tipologi penelitian preskriptif yaitu melakukan pendekatan secara intensif, mendalam dan mendetail serta komprehensif untuk menggali secara mendalam mengenai masalah penelitian. Hasil penelitian menunjukkan bahwa sepanjang pemilihan umum di era reformasi, diberlakukan berbagai aturan seputar ambang batas dalam rangka mewujudkan multipartai sederhana dan stabilitas presidensial, aturan tersebut berupa syarat pendirian partai politik, syarat partai politik mengikuti pemilihan umum, ambang batas perolehan suara untuk dapat mengikuti pemilihan umum berikutnya (electoral threshold), ambang batas perolehan suara partai politik untuk duduk di parlemen (parliamentary threshold), ambang batas pembentukan fraksi (fractional threshold), ambang batas pencalonan presiden (presidential threshold). Kebijakan penetapan ambang batas berakibat hukum: 1)Partai Politik tidak diakui sebagai badan hukum; 2) Partai Politik tidak dapat menjadi peserta pemilu; 3)Partai Politik tidak dapat memperoleh kursi di DPR. Meskipun syarat pendirian partai, pendaftaran partai sebagai badan hukum, serta syarat partai untuk mengikuti pemilu telah efektif menurunkan jumlah partai politik, namun penetapan ambang batas electoral threshold telah gagal dalam praktik disebabkan oleh jumlah partai melakukan fusi terbilang rendah dan kebijakan parliamentary threshold yang tiap tahun semakin tinggi, namun jumlah partai politik di parlemen masih berada pada kondisi multipartai ekstrim.

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This thesis discusses the Threshold Mechanism for the Stability of the Presidential System and the Simple Multiparty System in Indonesia, with the aim of knowing concretely the essential conditions for the realization of an effective presidential government, through the substance of the policy setting limits in force in Indonesia, and the implications of setting thresholds on the stability of Indonesias presidential and multiparty systems. This research was conducted using normative legal research methods, through library research, with prescriptive research typologies that are conducting intensive, in-depth and detailed and comprehensive approaches to explore deeply about research issues. The results showed that during the general election in the reform era, various rules around thresholds were imposed in order to realize simple multiparty and presidential stability, the rules were in the form of the requirements for the establishment of political parties, the requirements for political parties to participate in general elections, the threshold for votes to be able to participate in general elections next (electoral threshold), the threshold of the vote acquisition of political parties to sit in parliament (parliamentary threshold), the threshold for fraction formation (fractional threshold), the threshold for presidential nomination (presidential threshold). The policy to determine the threshold has legal consequences: 1) Political parties are not recognized as legal entities; 2) Political parties cannot participate in the election; 3) Political Parties cannot obtain seats in the DPR. Although the requirements for party establishment, party registration as a legal entity, and party requirements for participating in elections have effectively reduced the number of political parties, the electoral threshold has failed in practice because the number of parties fused is relatively low and the parliamentary threshold policy is getting worse every year high, but the number of political parties in parliament is still in extreme multiparty conditions.