The etiology of many neurological and neuromuscular disorders is largely unknown. Contributions likely come from both inherited and environmental factors. Amyotrophic lateral sclerosis ("ALS") is a prototypical example. In 5-10% of cases, genetic mutations exert a strong enough influence on disease development that the syndrome is transmitted in a clearly Mendelian fashion. Investigations in these "familial" ALS cases have identified more than 20 causative disease genes. Intensive study of these genes has helped identify several key cellular pathways as important for disease, not only in cases with obvious gene mutations, but even in the 90% of ALS cases that appear to be "sporadic." Further insights have come from investigating blood biomarkers in ALS such as gene and protein expression and lymphocyte profiling. It is hoped that further genetic and biomarker analysis will identify additional genetic risk factors or biomarkers to better understand the disease and improve therapeutic development. These advances can be applied not just to ALS but to the broad range of neurological and neuromuscular diseases, including Charcot Marie Tooth neuropathy, the muscular dystrophies, epilepsies, Parkinson's disease, and Alzheimer's disease.