Motor neuron diseases (MNDs) are a group of progressive neurodegenerative disorders associated with the degradation of the upper (UMN) or lower motor neurons (LMN) or both. They encompass amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), spinobulbar muscular atrophy (SBMA), hereditary spastic paraparesis (HSP), and others. MND patients present with a wide variety of clinical symptoms, including muscular weakness, atrophy, and corticospinal tract signs in diverse combinations. Over recent years, considerable collaborative efforts have been made to unravel the underlying pathophysiology of MNDs and find novel therapeutic interventions. With this book, we aim to provide both professionals and the general public with an outline of the latest scientific advances regarding the genetics, pathophysiology, diagnostics, and treatment options for MNDs. Researchers from different parts of the world have contributed to this volume in order to create a comprehensive multidisciplinary overview of the topics.