Earthworms inhabit wide range of soils representing 60-80% of the total soil biomass. Earthworms when present in soil inevitably work as ‘soil conditioners’ to improve its total physical, chemical and biological properties, as well as its nutritive value for healthy plant growth and high productivity. This is done by soil fragmentation and a breakdown of organic matter in soil and release of nutrients, secretion of plant growth hormones, proliferation of ‘nitrogen-fixing and phosphate solubilizing’ bacteria, increasing biological resistance in crop plants, and all these worm activities contribute to improved crop productivity. This book presents and discusses research in the study of earthworms as soil managers.