Nematodes are small multicellular organisms that have been used as biological models since the 1960s. For example, Caenorhabditis elegans is a free-living nematode worm, about 1mm in length, that lives in temperate soil environments. It is made up of about 1000 cells, and has a short life cycle of only two weeks. It was the first multicellular organism to have its whole genome sequenced. The book summarizes the importance of nematodes as model organisms in the fields of genetics, developmental biology, neurobiology, pharmacology, nutrition, ecology and parasitology. Of interest to a broad audience across a wide spectrum of disciplines, this book is useful for biologists working on comparative studies to investigate biological processes across organisms; medical scientists and pharmacologists for exploration of drugs and medicine (including the use of genome editing to eliminate diseases); ecologists considering nematodes as indicators for environment changes; and parasitologists for host-parasite interactions. Many other researchers can use this book as a benchmark for the broad implications of nematology research on other aspects of science.