Safe diving demands a minimum team of four or more members, each equipped with heavy apparatus and supported by boats, compressors, recompression chambers and other heavy plant. When travelling abroad, underwater ex? plorers must either organize a self-contained expedition equipped with all the necessary facilities, or plan to travel alone, diving at sites where local facilities and diving partners are to be found. This article provides hints for the serious underwater explorer who wants to travel light. Among the topics considered are: equipment, certificates, insurance, legal problems, air freight and customs, surveying with simple instruments, photography. The aim here is to supple? ment the many excellent manuals concerned with specific diving techniques and the Underwater Association's Code of Practice for Scientific Diving. These notes have been prepared to guide the qualified diver setting out alone, or with just one or two companions, to dive abroad. The aim has not been to advise those planning a self-sufficient diving expedition, but rather to indicate how the small group can live off the land by diving with local groups and by relying on local recompression chambers, boats and compressed air. It is possible to travel light yet enjoy all the resources of large diving groups. The hints have been prepared with the serious underwater explorer and researcher in mind. The reason for travelling will vary from reader to reader. Some will find a lifetime's work in one single site (for example, Walter Starck's work on fishes at Alligator Reef, Florida) and after their initial search for the ideal locality will settle into an efficient working relationship with the local diving community. Others will need to travel extensively in search of a wide range of sites for comparative study (for example, Dr. N. C. Flemming's collection of archaeological evidence for sea level changes in the Mediterranean); they have to make new contacts at each site along their journey. Some readers will be travelling along popular holiday coasts where tourist facilities abound; others will travel to distant localities where divers are not accustomed to receiving visitors. In general there is less need for underwater explorers to travel to remote areas than for their terrestrial peers. The limited ranges of visibility and mobility below the surface force the diver to become a miniaturist, and the sea is so rich in life that sites covering only a small area by terrestrial standards may merit years of study underwater. There is much muddled thinking about the choice of an area to explore underwater. The false identification of underwater explorers as a branch of the main stream of terrestrial exploration often leads beginners to burden themselves with journeys to difficult sites requiring complicated logistic support. Often these remote areas offer no greater challenge under the sea than more accessible regions. The problems asso? ciated with working seriously underwater provide a sufficient challenge without adding tedious expedition logistics. These notes, then, are intended to help the reader overcome two major problems which confront him when he plans to travel abroad either alone or with just one or two companions. The first arises from the potential hazards inherent in all diving. Diving is not dangerous provided those involved are well-trained and have sufficient experience for the ambient working conditions (depth, visibility, currents, sea state, etc.) and provided that they follow the procedures recommended in the appropriate Manuals and Codes of Practice. Problems arise when the traveller's programme of ?^ John Woods, a member ofthe Society's Expeditions Committee, is Professor of Physical Oceanography at Southampton University. He is also Scientific Officer of the British SubAqua Club and co-editor of Underwater Science: an introduction to experiments by divers, published in 1971. This is the first of a series of papers on matters relating to expeditions.