Abstract: The one of some problems faced by Moslems in Indonesia is about how to determine the beginning of month of hijri year. It happens because there is no agreement on the criteria of the beginning of month of hijri year. The different ways on the interpreting hadith about the beginning of the month causes emerged of two different streams. On one side, there are some Moslems who use rukyat method (seeing the new moon) as the best way to determine the beginning of the month, usually called as “madzhab rukyat”. On the other side, there are also some Moslems who prefer to use hisab method (counting the position of the new moon) as the best way to determine the beginning of the month, usually called as “madzhab Hisab”. This difference has lead to a discordance among Moslems because it take effect on the way to determine the beginning of Ramadhan, the beginning of Syawal, and determine time to doing Arafah fasting. This article is trying to identify the root of that difference. There is the fact that there are also the new differences which made the gap within each method, so it becomes wider than before. Abstrak: Penentuan awal bulan Hijriyah merupakan salah satu di antara permasalahan yang ada di kalangan umat Islam di Indonesia. Permasalahan ini terjadi karena belum disepakatinya kriteria awal bulan. Perbedaan penafsiran terhadap hadits tentang awal bulan menyebabkan terdapat dua aliran yang berbeda. Di satu sisi, ada sekelompok umat Islam yang menggunakan metode rukyat yang biasanya disebut dengan madzhab  rukyat. Di sisi lain, ada juga sebagian umat Islam yang lebih memilih memakai metode hisab, yang kadang dinamakan sebagai madzhab hisab. Perbedaan metode penentuan awal bulan ini kadang menimbulkan perpecahan di kalangan umat Islam karena berkaitan dengan penentuan awal Ramadhan, awal Syawal, dan puasa Arafah. Artikel ini berusaha mengkaji akar perbedaan yang memunculkan metode hisab dan rukyat dalam penentuan awal bulan Hijriyah. Perbedaan antara metode hisab dan metode rukyat semakin bertambah ketika masing-masing dalam metode tersebut pada kenyataannya juga memiliki perbedaan.