Israel perceives itself to be under a constant and general threat to its existence. Like many other aspects of its security, Israel’s small size relative to its neighbors means that even relatively small demographic shifts may have unexpected and threatening political consequences. Israel’s struggles with security, identity, and demography therefore serve to highlight a relationship not unique to Israel but particularly intense there: a relationship between demographic shifts and state, regional, and interstate security. This article demonstrates that Israel’s demographic shifts have come to be regarded as an existential threat by Israel, and the contemporary salience of demography in Israel explains both (1) Israel’s decision to build a ‘security fence’ between it and the Palestinian Occupied Territories in the West Bank, and (2) the timing of that decision. The article examines Israel’s historical demographic trends and discourse and makes the case that this high-level national policy was a response to the perception among Israel’s leaders that demographic threats to both the Jewish and democratic character of Israel were more grave even than the physical threat of terrorism. © 2012, SAGE Publications. All rights reserved.