It is now well known that the mid-ocean flow is almost everywhere domi­ nated by so-called synoptic or meso-scale eddies, rotating about nearly vertical axes and extending throughout the water column. A typical mid­ ocean horizontal scale is 100 km and a time scale is 100 days: these meso­ scale eddies have swirl speeds of order 10 cm s -1 which are usually con­ siderably greater than the long-term average flow. Many types of eddies with somewhat different scales and characteristics have been identified. The existence of such eddies was suspected by navigators more than a century ago and confirmed by the world of C. O'D. Iselin and V. B. Stock­ man in the 1930's. Measurements from RIV Aries in 1959/60, using the then newly developed neutrally buoyant floats, indicated the main char­ acteristics of the eddies in the deep ocean of the NW Atlantic while a se­ ries of Soviet moored current-meter arrays culminated, in POLYGON- 1970, in the explicit mapping of an energetic anticyclonic eddy in the tropical NE Atlantic. In 1973 a large collaborative (mainly U. S. , U. K. ) program, MODE-I, produced synoptic charts for an area of the NW At­ lantic and confirmed the existence of an open ocean eddy field and es­ tablished its characteristics. Meso-scale eddies are now known to be of interest and importance to marine chemists and biologists as well as to physical oceanographers and meteorologists.