Amyotrophic lateral sclerosis is a fatal neurodegenerative disease of the upper and lower motor neuron of unknown etiology. Although a familial cause for this disease has been suspected early one, it is only in the past two decades that advances in modern genetics led to the identification of more than 10 genes linked to familial ALS and helped us understand some of the complex genetic and environmental interactions that may contribute to sporadic ALS. In this article, we chronologically summarize the genetic breakthroughs in familial and sporadic ALS and depict how it shaped our understanding of disease pathogenesis and our quest for rational therapies.