Recent innovations in cognitive neuroscience have advanced understanding of the neurobiological foundations of fluid intelligence (Gf) and adaptive reasoning and problem solving (ARP). Rather than engaging a single brain structure (e.g., prefrontal cortex) or operating at a fixed level of performance throughout adulthood, emerging neuroscience evidence indicates that Gf and ARP are mediated by a distributed neural system whose functions can be significantly enhanced by specific types of interventions, including cognitive training, high-definition transcranial direct-current brain stimulation (HD-tDCS), and physical fitness training. The main objective of the INSIGHT project is to establish and validate a comprehensive and rigorous brain training protocol that incorporates the best available interventions for the enhancement of Gf and ARP.