Abstract
This article discusses the need to clarify the circumstances in which it is lawful to place a person under immediate detention or restraint in a psychiatric emergency in New Zealand. The author identifies the full range of sources of authority or justification that are recognised in New Zealand for the immediate arrest or detention of a mentally disordered person, before analysing the meaning of detention in each of these circumstances, and the statutory powers and common law justifications for detention. The article concludes that common law justifications for the detention of mentally disordered persons continue in New Zealand around the margins of the statutory schemes.