This study examines the defence of duress in the criminal law. The first two chapters are concerned with the problem of what acts can be considered to have been performed under duress. An analysis of coerced acts is undertaken from the point of view of the philosophy of action. The legal treatment of the defence begins with a discussion of its juridical basis. On what grounds have the courts regarded duress as a defence? The question of whether it affects mens rea is discussed. This is followed by an analysis of the nature of the threat required to establish the defence. Modern developments in the cases are discussed, attention being drawn to an emerging liberal view of the law in this area. Finally, two issues raising moral problems are considered. The first of these is the requirement of the prior innocence of the accused; the second is the vexed question of duress and murder. Can one take life under duress and still claim the defence? Recent important decisions on this matter are scrutinised.