New genetic technologies are transforming nervous system studies in mice, impacting fields from neural development to the neurobiology of disease. Of necessity, alongside these methodological advances, new concepts are taking shape with respect to both vocabulary and form. Here we review aspects of both burgeoning areas. Presented are technologies which, by co-opting site-specific recombinase systems, enable select genes to be turned on or off in specific brain cells of otherwise undisturbed mouse embryos or adults. Manipulated genes can be endogenous loci or inserted transgenes encoding reporter, sensor, or effector molecules, making it now possible to assess not only gene function, but also cell function, origin, fate, connectivity, and behavioral output. From these methodological advances, a new form of molecular neuroscience is emerging that may be said to lean on the concepts of genetic access, genetic lineage, and genetic anatomy – the three ‘Gs’ – much like a general education rests on the basics of reading, ‘riting and ‘rithmetic.