Among the different agents which cause diseases in plants, viruses are considered next to fungi and nematodes in terms of economic crop losses induced by them. However, in the Arab countries, losses caused by viruses are likely to cause greater economic losses than is recognized, because the nature of the losses and the skills needed to identify the causal agents are different from those caused by fungi, bacteria and nematodes. The economic importance of a virus on a specific crop varies widely, depending on the availability of (i) inoculum source, (ii) virus vector, (iii) susceptible cultivars, and (iv) conducive environmental conditions. It is fortunate that not all viruses that affect a certain crop are present in one region. In spite of the absence of reliable loss data on many virus diseases in the Arab countries, it is generally accepted that many of them are of major production constraint. Such major viruses include the Luteoviruses which infect cereal and legume crops Citrus tristeza virus on citrus Grapevine fanleaf virus and Grapevine leafroll-associated viruses on grapes Maize dwarf mosaic virus in maize Tomato yellow leaf curl virus on tomatoes Zucchini yellow mosaic virus on cucurbits Potato virus Y and Potato leaf roll virus on potatoes and Prunus necrotic ringspot virus, Prune dwarf virus and Plum pox virus on stone fruits. Actual losses have been reduced due to the progress made over the last two decades in developing resistant varieties or improved management practices. Such improvements are not reflected yet in the loss data available, which is in many instances very old. In some Arab countries, facilities for proper identification are lacking and identification is based only on field diagnosis and indexing on indicator plants. Development of integrated control measures by combining sanitation, genetic resistance and other agricultural practices to control virus diseases in some important crops is urgently needed.For more details on Plant Viruses in the Arab Region, please see the virology book which published by Arab Society of Plant Protection