Energy consumption in our society is rapidly increasing, but nearly 60 % of the generated energy is wasted in the form of heat. Thermoelectric energy conversion has recently gained great attention as a viable technology to directly convert waste heat into electricity and thus enhance the energy efficiency. A new emerging application for thermoelectrics is harvesting energy from human body-heat on the skin using wearable thermoelectric power generators (TEGs). It has been recently demonstrated that these wearable TEGs can generate a few hundred microwatts level, which is enough to power a small bio sensor. In this talk, we overview recent advances in the development of thermoelectric materials and devices, and discuss the nanoscale transport physics behind the recent enhancement in thermoelectric materials performances. Various applications for thermoelectric energy conversion in waste heat recovery and energy harvesting are introduced. Challenges in further enhancing the thermoelectric performance of these materials and fabricating practical devices with scalable and cost-effective techniques are also discussed for future research directions.