Parasitic weeds, representing more than 4,000 species of more than 20 higher plant families, are one of the most destructive and intractable pests to agricultural production in both developed and developing countries. Parasitic weeds cause heavy damage to numerous crops by reducing both crop yield and quality. Yield losses could be estimated up to 30–80 % in staple food and industrial crops in every continent. In combination with other pests, they can reduce 100 % of crop productivity. Compared with the other weeds, parasitic weeds are difficult to control by conventional means due to their life style: Parasites are intimately involved with the host, and have so much metabolic overlap with the host that differential treatments are very difficult to develop. In some cases, the parasites are closely associated to the host root, concealed underground, and undiagnosed until they irreversibly damage the crop. Parasitic weeds, such as Broomrapes (Phelipanche/Orobanche spp.), Striga, and some Cuscuta spp., represent the most extreme examples of parasitism on host plants. This chapter summarizes the current knowledge on the biology and development of the above parasites, and effective approaches to parasitic weed management, which will include conventional and new biotechnology-based control measures against the major world pests Orobanche, Phelipanche, Striga, and Cuscuta.