The technique of controlled delivery is used when a consignment of illicit drugs is detected and allowed to go forward under the control and surveillance of law enforcement officers in order to secure evidence against the organizers of such illicit drug traffic. This technique has been proved effective in some countries in identifying and bringing to justice principals, organizers and financiers of the illicit drug traffic. The controlled delivery technique is compatible with the requirements of the Single Convention on Narcotic Drugs, 1961, but its application depends on the particular legal and administrative provisions in the countries concerned. The technique merits wider use, and it does not involve any element of entrapment. It has been used most effectively when illicit drugs are discovered in unaccompanied freight consignments or in the post. Controlled deliveries involving a courier present special difficulties and should be treated with caution. In a controlled delivery, security of information is of paramount importance as is the appropriate knowledge and co-operation of the law enforcement authorities. Such co-operation is essential between the country in which the initial detection of drugs has occurred, transit countries and the country of final destination. A number of important detections have been made as a result of speedy international co-operation of this type between law enforcement authorities.