Precise genome editing has transformed biology and is beginning to reshape medicine, yet translating these technologies to the brain remains a major challenge. In this seminar, I will present our efforts to develop compact, single AAV-delivered base editors and demonstrate their therapeutic potential in mouse and marmoset models of Rett syndrome, a severe neurodevelopmental disorder that primarily affects girls. Finally, I will discuss how these technologies establish a versatile toolbox for precision genetic medicine and functional genomics in the living brain.