Governments when faced with countering terrorism have a number of options at their disposal. One such option is the collection of intelligence, and human intelligence can provide valuable information on terrorist groups and their activities. ‘Tout’, ‘informer’, ‘informant’, ‘source’, ‘agent’, ‘grass’, ‘mole’ and ‘nark’ are some of the labels used to describe what law enforcement terms a Covert Human Intelligence Source. They are in fact individuals who provide information as part of a covert or secret arrangement. Informants, for that will be the descriptive term used for the purpose of this paper, are an interesting phenomenon in themselves, but even more so when considering their use in the context of the ‘Troubles’ in Northern Ireland. Informants undoubtedly played a role in countering terrorism during the period but remain the subject of controversy and fascination. Their presence served to provide intelligence, to disrupt activity and cause paranoia within terrorist ranks. This paper examines the rationale for their deployment, their utilization in Northern Ireland and the recruitment processes engaged in by the security forces. There will also be a discussion of the ethical and legal dilemmas faced by law enforcement and intelligence gathering agencies engaged in their use.