Amyotrophic lateral sclerosis (ALS) is a devastating paralytic disorder caused by motor neuron degeneration. A subgroup of familial cases arises from mutations in the gene encoding cytosolic superoxide dismutase (SOD1). This review considers insight now being gained into ALS pathogenesis from the study of mutant SOD1 protein and its possible mechanisms of adverse effect on nerve cells. Also discussed are the status of other genetic forms of ALS and the elusive question of why this disorder so specifically targets motor neurons. Ultimately, it is hoped that insights from these types of studies will improve the prospects for developing meaningful therapies of ALS.