The work presented in this book consists of three disparate elements which have the unifying feature of being concerned with alphasatellite. The satellite-like alphasatellites (previously known as DNA 1) were first identified in 1999 and were shown to be associated with the majority of begomoviruses (family Geminiviridae) that require the satellite molecule now collectively known as betasatellites. Virus-induced gene silencing (VIGS) is a powerful reverse genetics tool for application in functional genomics. The alphasatellite-based VIGS vector was shown to be functional by silencing expression of GFP in 16c plants and magnesium chelatase. In addition, the alphasatellite vector was shown to be useful as a gene expression vector. An analysis of tomato plants from Oman exhibiting severe leaf curl symptoms showed the presence of Tomato yellow leaf curl-Oman (TYLCV-Om), a virus previously shown to be present in tomato in this country, a new recombinant begomovirus species, for which the name Tomato leaf curl Oman virus (ToLCOMV) is proposed, a betasatellite (tobacco leaf curl betasatellite (TbLCB) and an unusual alphasatellite. The significance of these findings is discussed.