There is great hope to tackle serious global issues related to energy consumption and waste by developing technologies based on efficient nanoscale materials and devices. For this to happen, we need breakthroughs in our ability to control electrical and thermal transport at the nanoscale. Ab-initio materials modelling will play a central role in this, providing microscopic understanding and the materials parameters needed to bridge the macroscopic performance and the microscopic mechanisms that determine transport properties. In this project I will use ab initio techniques based on density-functional theory to calculate the electronic and vibrational properties of materials as well as the carriers' relaxation times due to carrier-carrier and carrier-defect interactions. These are the key ingredients that will then be used in the Boltzmann transport equation to simulate transport in devices, taking into full account the coupled electron-phonon dynamics in complex geometries, and in the presence of interfaces or defects. The research will proceed in three main directions. First, toward engineering materials and devices for high-performance nanoelectronic applications. Here I will study the detailed mechanisms of carrier-induced heating in silicon- and carbon-based electronic devices: this is a key technological issue that is becoming dominant as we race toward the nanoscale. Second, toward identifying new optimal thermoelectric materials, which are of great relevance to energy conversion or cooling applications. To this end, I will perform a systematic study of the thermoelectric properties of promising materials, starting from ternary and filled CoSb3-based skutterudites. Third, toward characterizing structural and spectroscopic properties of materials and devices. Here I will place particular effort in building a database of thermo-mechanical and spectroscopic properties of the materials that show the most promising transport characteristics.