Genetic therapy covers a range of methods for modifying the nervous system, including delivery of genes, sequence-targeted regulatory molecules, genetically modified cells and oligonucleotides. In this review, we focus on ways to change the genetic status of the nervous system, including routes of access and modes of delivery. Examples are provided of strategies used for a number of diseases, including recessive loss of function conditions [lysosomal storage diseases and spinal muscular atrophy (SMA)], dominant toxic mutations [amyotrophic lateral sclerosis (ALS)] and conditions of mixed etiology [Alzheimer's disease (AD), Parkinson's disease (PD) and brain tumors] (Fig. 1). Neurodegenerative diseases caused by triplet nucleotide repeats are discussed in an article on siRNAs in this issue. Many of these strategies have proven very promising in preclinical studies in mouse and larger animal models, and a substantial number are now being evaluated in clinical trials.