According to Orthodox Judaism, Jewish law today is based on the commandments in the Torah, as viewed through the discussions and debates contained in classical rabbinic literature, especially the Mishnah and the Talmud. Orthodox Judaism thus holds that the halakha represents the "will of God", either directly, or as closely to directly as possible. The laws are from the word of God in the Torah, using a set of rules also revealed by God to Moses on Mount Sinai, and have been derived with the utmost accuracy and care, and thus the Oral Law is considered to be no less the word of God. If some of the details of Jewish law may have been lost over the millennia, they were reconstructed in accordance with internally consistent rules; see The 13 rules by which Jewish law was derived.
Where were the rules about the Torah revealed to Moses by God?
Mount Sinai