Axons are neuronal output elements responsible for the transfer and processing of signals from one neuron to another, even over very large distances. For a given neuronal cell type, axons are unique and display heterogeneous patterns in terms of shape, length, and target structure. Axons are the usually long processes of a nerve fiber that generally conduct impulses away from the body of the nerve cell. This book aims to summarize recent findings covering morphological, physiological, developmental, computational, and pathophysiological aspects of axons. It attempts to address new findings concerning axonal structure and functions, their implications for signal transduction, processes involved in the formation of axonal arbors, and the transport of subcellular elements to their targets, as well as how dysfunction in one or several of these steps could occur.