Chemotaxis is the phenomenon in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules, or to flee from poisons. In multicellular organisms, chemotaxis is critical to early and subsequent phases of development, as well as in normal function. This book discusses research in the study of chemotaxis including the cell migration signalosome, the role of chemotaxis in the association of the azospirillum brasilense plant, the role of CD46 in the control of chemotaxis of activated T cells in MS pathogenesis and the regulation of chemotaxis by heterotrimeric G proteins.