Abstract: Thermoelectric energy conversion technology is a clean-energy technology, which can convert energy directly between heat and electricity using thermoelectric materials. The conversion efficiency is mainly determined by the performance of the material, which includes the electrical and thermal transport properties. Asuitable balance between the latter must be found to optimize the thermoelectric properties. This paper describes recent developments in minimizing the heat conduction in thermoelectric materials and micro-devices, focussing on the effect of wide-spectrum phonon scattering and the damping of phonon transverse waves in semiconductor compounds, and phonon scattering by the interfaces and defects in low-dimension structures and thermoelectric composites. Finally, an overview of recent advances in high performance thermoelectric micro-devices improved by the suppression of heat conduction around room temperature will be given.