Study of parasitology, like any other branch of biological science, has in recent years been increasingly revealing and rewarding with enrichment and embellishment by basic sciences, specially with application of spectacular advances in molecular biology and biotechnology. Such a fruitful fusion of more than one discipline has now come to characterise more than ever before our approach to the subject. This volume of helminthology with contributions from a galaxy of distinguished scientists in specific areas, bears an eloquent testimony to the gratifying yield that accrues from cross fertilisation of multiple disciplines and able support from basic sciences. Matazoan parasites, helminths, living in more than one host in different stages of development, present an intricate spectrum of host-parasite relationship, which has evolved through diverse frame and flow of ecologic circumstances. The situation is further complicated, as elaborated here, by genotypic and phenotypic variations, which profoundly influence the dynamic interaction between hosts and parasites and determine consequently survival and propagation of the latter. Indeed, one of the important messages upheld in this book is that genetic endowment of parasites plays a pivotal role in their immunogenicity, pathogenicity, response to variable environmental composition, including drug response and also their transmission dynamics and epidemiology. Evolution of parasitic helminths with concomitant physiologic and morphologic alterations have been traced from free-living stage to development of host-specificity of different degrees and parasitic speciation.