The biblical sources on the attack of Sennacherib of Assyria against Hezekiah of Judah are extensive and varied, bespeaking the major impact that attack had on Judaean society. The dominant feature of these biblical sources is surely the letter-address of Sennacherib, communicated by the king's officials, especially the rab šāqēh, to Hezekiah and his subjects in Jerusalem, and the latter's response. The present paper examines the several ways in which the Bible depicts this address and the response, in the course of considering an even more basic question: why such an address appears in the biblical sources at all. Though no one answer to this question appears fully satisfying, all have their place and value, as the paper tries to show. Equally, all testify, despite their differences, to the overwhelming challenge of the Assyrian Empire to Judah and the biblical authors, particularly in matters of self-identity, and the enduring significance of this challenge well beyond the particular events that inspired it.