ALS is a disease characterized by the progressive loss of upper and lower motor neurons leading to weakness and spasticity. Diagnosis of ALS is based on exclusion. ALS and frontotemporal dementia (FTD) constitute the extremes of the spectrum of one disease. Many patients show signs of both ALS and FTD. ALS is a heterogeneous disease in which multiple genetic factors contribute. More than 20 genes are known to play a role in ALS pathogenesis. In approximately 5-10% of cases the disease is familial with autosomal dominant inheritance. There is no curative treatment for ALS. The treatment of ALS patients is symptomatic and is focused on achieving a high level of quality of life. New insights into the genetic fundamentals of ALS offer hope for new therapies. Gene-targeted treatment strategies using antisense oligonucleotides are a promising development.