Publisher Summary This chapter discusses development of vaccines against helminth parasites. Progress toward the development of vaccines against helminth parasites has been disappointing. In some respects, this is surprising as the first commercial vaccine against a helminth infection, parasitic bronchitis of cattle, was introduced nearly 30 years ago, following the demonstration that exposure to living radiation attenuated infective larvae of the nematode dictyocaulus viviparus induced a powerful resistance against the disease. This vaccine is 98% effective in the field, and it is the only practical method of preventing this damaging and expensive disease. A second radiation-attenuated vaccine, against another nematode, the dog hookworm, Ancylostoma caninum, has been exposed to reach the efficiency necessary for commercial development and field use, and it was marketed in the United States in 1973. It did not provide the commercial success expected as veterinarians preferred, instead, to manage hookworm disease by drug treatment. Some success has also been achieved in vaccination of cattle and buffaloes against the blood flukes Schistosoma bovis, and S. japonicum, with live, attenuated larvae.