Josiah ( or ) or Yoshiyahu was the 16th king of Judah (c. 640–609 BCE) who, according to the Hebrew Bible, instituted major religious reforms by removing official worship of gods other than Yahweh. Josiah is credited by most biblical scholars with having established or compiled important Hebrew scriptures during the "Deuteronomic reform" which probably occurred during his rule. Josiah became king of the Kingdom of Judah at the age of eight, after the assassination of his father, King Amon. Josiah reigned for 31 years, from 641/640 to 610/609 BCE.

Josiah is known only from biblical texts; no reference to him exists in other surviving texts of the period from Egypt or Babylon, and no clear archaeological evidence, such as inscriptions bearing his name, has ever been found. However, a seal bearing the name "Nathan-melech," the name of an administrative official under King Josiah according to 2 Kings 23:11, dating to the 8th century BCE, was found in situ in an archeological site in Jerusalem. Some scholars believe this seal represents the individual mentioned in 2 Kings 23:11. Additionally, most scholars believe that Josiah existed historically and that the absence of documents is due to few documents of any sort surviving from this period, and to Jerusalem having been occupied, conquered, and rebuilt over thousands of years.