The security sector of a state-that cluster of organs with direct responsibility for internal and external security-can be viewed as the state's inner core, the locus of ultimate state power. Under normal conditions, security systems enjoy substantial autonomy and insulation from accountability and pressure group influence.' Outside actors typically have little information about and access to this sphere. These realities tend to make security institutions the least amenable of any state organs to fundamental transformation. This does not imply that these agencies are immune to modification and innovation, but suggests that far-reaching change is rare, especially in a highly repressive internal security apparatus. Northern Ireland (or Ulster) is particularly interesting in this regard because it has been the site of a protracted struggle to defend, refashion, and dissolve the basic policies and institutional foundations of internal security. Along with the conflict over the constitutional status of the province, security matters have been perhaps the most vehemently contested of all issues. But despite the fact that the security core has become such an object of struggle, it remains relatively autonomous and unresponsive to direct social pressures. How can this state of affairs be explained? The British government, which took power from Northern Ireland's Protestant-dominated Unionist government in 1972, has consistently hinged any further liberalization of the system of control on the defeat of political violence.2 Yet, although violence is certainly a central feature of the trauma of Northern Ireland, it is not necessarily the chief determinant of the character of security arrangements there. Political violence has steadily diminished over the past fifteen years, yet several of the more illiberal features of the security enterprise have become only more firmly institutionalized.3 Political conditions may have at least as great an impact on the character of a security system as the persistence of violence and unrest.4 This article therefore examines the ongoing struggle in Northern Ireland to shape internal security policies and structures in terms of three factors: (1) regime priorities and capacities, (2) the influence of organized party pressure, particularly that of the Protestant Unionist parties,5 and (3) the impact of collective protest and resistance. I will suggest that the existing security system reflects the short-term interests and objectives primarily of the British state, but also that the state's capacity to act is constrained to some extent by popular Protestant (or loyalist) and Catholic (or nationalist) forces.6 This analysis will also shed light on the larger question of the distinctive character of British rule in Northern Ireland, an issue that has not received sufficient scholarly attention.