In the wake of the Second World War and the realisation that the Soviet Union had set up extensive espionage networks around the world, Australia responded by establishing its own spy-hunting agency: ASIO. By the 1950s its counterespionage activities were increasingly supplemented by attempts at countersubversion-identifying individuals and organisations suspected of activities that threatened national security. In doing so, it crossed the boundary from being a professional agency that collected, evaluated, and transmitted intelligence, to a sometimes politicised but always shadowy presence, monitoring not just communists but also peace activists, scientists, academics, journalists, and writers. The human cost of ASIO's monitoring of domestic dissenters is difficult to measure. It is only through recovering the hidden histories of personal damage inflicted by ASIO on both lawful protesters and, in some cases, its own agents, that the extent can be revealed.