In broad terms, the prosecution in a criminal case bears the burden of proving not only that the defendant acted with the relevant fault ingredient for the individuated crime in question, but also to disprove any defence in support of which evidence is propounded. Defences apply consequentially to ensure that only the blameworthy are punished in accordance with culpability thresholds, and that blameless individuals are not unjustly punished for propagating a social harm. Exculpatory evidence may be adduced as justification (necessity or self-defence), by way of total excuse (duress or insane automatism), potentially as partial excuse (intoxication or diminished responsibility), or mitigation. General defences have developed in England and Wales in a solipsistic ad-hoc manner, and haphazardly rather than in a coherent structure. Extant law reveals significant problems in adoption of consistent approaches to doctrinal and theoretical underpinnings of general defences. This has been exemplified by a plethora of recent jurisprudential authorities revealing varying degrees of confusion and vacillation. A variety of Law Commission proposals for bespoke defences, although emboldening the debate, have yet to be adopted in any logical template. This book’s chapters by individual contributors, domestic and comparative, explore the fundamental precepts of general defences and cover a range of key issues within the spectrum of exculpatory behaviour. This includes England and Wales, Scotland and Ireland, as well as alternative approaches from several foreign jurisdictions. In Chapter 1, ‘How Criminal Defences Work’, William Wilson considers the various attempts made to establish some core unifying rationale to criminal defences capable of providing a blueprint for both their development and constituent elements. In this chapter, it is argued that it may be more helpful to draw attention to those constant elements in the constitution of criminal defences which quite understandably, if erroneously, have lent support to the view there is a unified rationale rather than a collection of different claims to avoid punishment. These constant elements typically include requirements such as reasonableness, immediacy, and a triggering condition, which serve to distinguish true defences from quasi-defences rooted in the defendant’s personality or psychological make-up. Crucially, these constant elements support the alternative view that the various rationales of criminal defences complement, rather than compete with, each other. They create the conditions by which the actor may support the actor’s claim that his conduct was justified; that he lacked the capacity or fair opportunity of conforming to the standards demanded; that he did not betray the standards of character which we have come to expect of ordinary decent citizens; or that his conduct was truly out of character. Bob Sullivan, in Chapter 2, ‘Avoiding Criminal Liability and Excessive Punishment for Persons Who Lack Culpability: What Can and Should Be Done?’, argues that a finding of culpability requires proof that the defendant (D) stands in some form of blameworthy relationship with a wrong. A wrong requires some setback or threat of imminent setback to the legally protected interests of individuals, organisations, or society at large. (The wide ranging content of modern criminal law includes many offences which may be committed without instantiating a wrong in the sense identified above. These offences fall beyond the scope of the chapter. Offences of strict liability which encompass wrongs in the sense identified above are within the scope of the chapter.) Situations will arise where D appears to be in some form of blameworthy relationship with a criminal wrong. To deflect findings that he was culpable, he may claim that defining elements of the wrong were not present, or that aspects of his personhood undermine any blame for his wrongs, or that because of the circumstances in which he found himself, conformity with the criminal law was not to be expected. Alternatively, he may assert that what ordinarily would constitute a wrong was in the circumstances the right thing to do. The scope and content of the general defences made available under English criminal law will be assessed in terms of their reliability as indicators of non-culpability for wrongs. Cases of underinclusiveness will be identified and some inclusionary proposals will be made. However, not all forms of non-culpability can be accommodated within a rule based system of criminal law.