Cucurbits are widely grown worldwide in diverse agroecosystems, from traditional gardens to soil-less glasshouses. Viruses represent one of the major threats for cucurbit production, affecting both the yield and quality of crops. The number of known cucurbit-infecting virus species has grown from 35 in 1998 to more than 80 in 2018. The prevalence and agronomic impact of these viruses are highly contrasted, and the major problems at the worldwide level are related to circa 10 virus species, both « classic » -i.e known for decades- or recently emerged on a large scale. Among the « old » mosaic-inducing viruses, aphid-transmitted viruses (potyviruses, cucumber mosaic virus) remain agronomically important, particularly in temperate climates. Despite their long-term prevalence and apparent stability, introductions of new strains have been observed in several countries in the last years, probably via commercial exchanges of plant material. Some of these introduced strains have rapidly replaced preexisting virus populations, sometimes resulting in an increased economical impact. In Mediterranean and tropical climates, as well as in heated greenhouses in temperate regions, Bemisia tabaci-transmitted viruses (begomoviruses, ipomoviruses, criniviruses) now constitute major problems. Their rapid emergence can be explained by the combination of changes in climate and cultural practices that favour their natural vectors, and the increased exchanges of plant material that made possible their long-distance spread. Viruses transmitted by seeds or by contact are also easily disseminated worldwide and represent important constraints for exchanges of plants or genetic material. Accurate and regular re-evaluation of the complex viral pathosystem infecting cucurbits in different countries, adaptation of cultural practices and development of resistant cultivars contribute to the continuous arm race against the introductions and local evolution of virus populations.