In Jewish law, a posek is a legal scholar who determines the application of halakha, the Jewish religious laws derived from the written and Oral Torah in cases of Jewish law where previous authorities are inconclusive, or in those situations where no clear halakhic precedent exists.

Halakha, also transliterated as halacha, halakhah, and halocho, is the collective body of Jewish religious laws that are derived from the Written and Oral Torah. Halakha is based on biblical commandments (mitzvot), subsequent Talmudic and rabbinic laws, and the customs and traditions which were compiled in the many books such as the Shulchan Aruch. Halakha is often translated as "Jewish law", although a more literal translation of it might be "the way to behave" or "the way of walking". The word is derived from the root which means "to behave". Halakha not only guides religious practices and beliefs, it also guides numerous aspects of day-to-day life.