A major problem for developmental science is understanding how the cognitive and emotional networks important in carrying out mental processes can be related to individual differences. The last five years have seen major advances in establishing links between alleles of specific genes and the neural networks underlying aspects of attention. These findings have the potential of illuminating important aspects of normal development and its pathologies. We need to learn how genes and experience combine to influence the structure of neural networks and the efficiency with which they are exercised. Methods for addressing these issues are central to progress in the decade ahead.