This document provides a review of amyotrophic lateral sclerosis (ALS). It begins with an introduction that defines ALS and discusses its classification. It then covers the epidemiology, clinical features, diagnosis, etiology, pathogenesis, and differential diagnosis of ALS. Some key points include that ALS is a rare neurodegenerative disease that causes motor neuron death and muscle paralysis. It can be sporadic or familial. Common symptoms include muscle weakness, spasticity, and difficulty speaking, swallowing, or breathing. The cause is largely unknown but may involve genetic mutations, oxidative stress, protein misfolding, or mitochondrial dysfunction.