This chapter deals with the internment of political prisoners in Northern Ireland during the 1920s. It is clear from the extensive police and ministry files that through observation, local knowledge, infiltration and informers, the Irish Republican Army (IRA) and Sinn Féin activities were closely watched and individuals’ movements and contacts were kept under constant review. Raids and arrests commenced on the night of 22/3 May 1922. Within a few weeks almost 300 persons – almost all Roman Catholic males – were detained; however, very few women were detained. Given Northern Ireland’s very limited prison accommodation, the search for custodial places was urgent. The scale of internment, the urgency of implementation, the pinched and makeshift nature of accommodation and the largely untrained warder staff all created management problems. The regime for internees was more liberal than that for remand prisoners such as own clothes, no prison labour, a liberal allowance of letters.