This cluster of papers focuses on the molecular mechanisms, genetics, and pathology of Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). It covers topics such as TDP-43, FUS/TLS, C9ORF72 mutations, neurodegeneration of motor neurons, RNA processing, progranulin deficiency, ubiquitin-positive inclusions, and the genetic underpinnings of these diseases.