Adeno-associated viral (AAV) vectors are the most frequently used gene-transfer tools in the study of the brain and spinal cord, which together are known as the central nervous system (CNS). AAVs are popular tools because: 1) their genomes are easy to manipulate, 2) they have long-term expression; and 3) they have limited toxicity. However, a key challenge of using AAVs for neuroscience research is the lack of a method for genetically manipulating neurons throughout the whole brain. Neurons of the peripheral nervous system (PNS), which connect the heart, lung, gut, and other organs to the CNS, are also an important target for gene delivery, especially for the study of pain. While many new capsids (i.e. the part of the virus that determines tropism) have been developed that increase transduction efficiency, none allow for simple and efficient transduction of both the CNS and PNS.That is until the Gradinaru Lab at Caltech stepped up to the challenge.