Permission in law for a veterinarian to exercise their professional judgement to prescribe unregistered or off-label antimicrobials in certain circumstances. In many countries, veterinarians must only prescribe antimicrobials that are registered for use in animals. However, this is not always possible or practical as there are few antimicrobials registered for use in certain animal species (e.g. fish) or for some uses of animals (e.g. dairy sheep). To strike a balance between legal prescribing requirements and the need to treat a wide range of conditions in animals, the laws in these countries permit the ‘prescribing cascade’.