The four papers which follow were read to a meeting of the Institute held at the Royal Geographical Society on 19 May. They provide an account of the four systems of radio position fixing that are most widely used at sea, and give both a description of the experience gained and a general survey of what has been achieved since the international meetings on radio aids to marine navigation were held in 1946 and 1947. Certain requirements for marine radio position fixing systems were formulated at these meetings and a measure of agreement was reached on the types of navigational aid which should be developed. This review of the four principal systems, and of aspects of some of them which may not be widely appreciated, may perhaps give an opportunity for assessing how much progress has been made over the last few years and of the problems that remain to be solved.