The Collision Regulations were long considered as sacrosanct and the question posed by this paper never arose. How to prevent collisions? Simply by applying the Regulations established for that purpose. Nevertheless a revision of the Regulations has been decided upon, to be undertaken by an international conference to be convened in 1972, and meanwhile many public and private bodies have applied themselves to the preliminary studies. As the author is not familiar with all the work now being done in this way a general review will not be attempted, but some thoughts on the subject arise from Commandant Robichon's paper ‘Reflections sur une enqu^tersquo; in the January 1970 issue of the Journal de la Marine Marchande and from the proceedings of the Working Party set up in the spring of 1970 by the Institute of Navigation, of which the author was a member.