Parasitology, the study of parasites and their relationships to their hosts, is one of the most fascinating areas of the biology. The parasitology has traditionally been limited to parasitic protozoa, platy helminthes and nemathelminthes, as well as those species of organisms that serve as vectors for parasites. But now a day it is approaching taxonomy, classical morphology, ultra topography, bioecology, epidemiology, molecular heterogeneity, phylogeny, biochemistry and in silico genome analysis to resolves it ambiguity in identification to biodiversity, biotechnology, and clinical diagnosis and health consequences. The protozoan and helminth parasites are fascinating organisms and examples of their parasitism are found in a broad range of hosts, including plants, invertebrates and vertebrates. The interaction between a parasite and its host is complex and dynamic. The scarcity of edited book designed for students and research scholars to use during dissertation or pre-doctoral programs of helmimthes Parasitology in northern India impelled me to produce this work in the form book. This book is written with the objective of providing fundamental knowledge concerning the taxonomy and influence of environmental factors on parasitic helminthes living systems. The book is written for those Graduate, Postgraduate and Researchers who need Morph taxonomic, Bio-ecological and Molecular phylogenetic information and assistance beyond that of an introductory text in general Parasiology. Author is very thankful to learned readers and request to send their valuable suggestions for further improvement of the book into possible future edition.