Although nematodes had long been suspected as vectors of soil borne plant diseases, unequivocal proof of their implication was not forthcoming until 1958 when Professor William Hewitt and his colleagues in California demonstrated experimentally that Xiphinema ~ was the vector of grapevine fanleaf virus. This opened up a new and exciting field in plant pathology and discoveries quickly followed of other nematode species associated with soil-borne diseases of many different crops and in several countries. After the initial enthusiasm of discovering new vectors and new viruses there followed a period of consolidation in which research workers sought answers to tantalising questions about the location of the virus within the nematode, the factors governing the close speci ficity between virus and vector; and more mundane but equally important and compelling questions about life cycles, geographical distribution, host relations, morphology and taxonomy. No other group of nematodes has attracted such a concentrated effort involv ing many different scientific specialisations and yielding so much progress in a relatively short time. The NATO Advanced Study Institute held at Riva dei Tessali, Italy, during 19 May to 2 June, 1974, provided the forum for a critical discussion of all aspects of biology of virus vector nema todes.