The study of musical disorders remains a rich, and perhaps unique, source of information regarding the brain organization underlying music cognition. Musical disorders reveal in vivo how musical abilities are organized by a process of reverse engineering. The study of musical disorders reveals causal and selective relations between brain and functions, while current neuroimaging techniques are mostly overinclusive and correlational. Moreover, the patient-based approach can be coupled to neuroimaging techniques to uncover unique links between musical abilities and the brain. In this presentation, I will focus on the detailed study of individuals who were born with severe musical problems. These disorders are particularly instructive because they have neurogenetic underpinnings. These disorders are termed “congenital amusia”, an umbrella term for lifelong musical disabilities that cannot be attributed to mental retardation, deafness, lack of exposure, or brain damage after birth. Congenital amusia provides a natural experiment—a rare chance to examine the biological basis of music by tracing causal links between genes, environment, brain, and behavior. I will present the main and most recent insights that the study of congenital amusia has provided on the biological foundations of music.