Surprise is a familiar term in military writings and is enshrined in most nations' doctrine. Surprises that emerge in tactics, however, can also operate at the strategic and operational levels and are particularly dangerous because they can test the relevance and adaptability of military forces and the 'institutional' defense establishments that create, develop, and sustain them. A military establishment that is too slow to recognize and respond to such surprises places its nation's interests at grave risk. Western nations are contemplating major reductions in defense spending, with consequent limitations on force structure. As the range of enemy capabilities that a force will be able to match, qualitatively and quantitatively, becomes smaller, the potential for operational and strategic surprise will increase. A key conclusion from this analysis is the critical role of strategic leadership in recognizing the scale of surprise and in forcing the necessary institutional response.