This book explores the foundations of the principle of altruism and its relationship to the criminal law, examining the contrasting justifications for the duty of easy rescue and the duty of tolerance, both of which are based on altruism. Since the days of Lord Macaulay and James FitzJames Stephen, it has been said that English law does not usually punish omissions, and that altruistic duties are incompatible with the spirit of the common law. This book aims to show that this is not an accurate description of English criminal law, and that there is a strong case to be made for the opposite understanding, based on principles advanced by authors such as Adam Smith, Jeremy Bentham, John Stuart Mill and others. By analysing the duty of easy rescue - which imposes on individuals a duty to take steps to rescue a person in danger if this can be done without risk to the rescuer, or at least a duty to call the emergency services - and by comparing it with the well-known duties arising in cases of extreme necessity, it can be shown that altruism has plenty to say in different parts of the criminal law. Having established the case for criminalising the failure to provide a simple rescue, a detailed analysis is made of the form that this criminalisation should take, bearing in mind the basic principles of English law and considering the strengths and weaknesses of the duty of easy rescue as it is formulated in various continental systems, including the German, French, Spanish and Italian criminal codes.