Wearable and mobile devices, such as smartphones, smartwatches, wearable medical devices, navigations and radios, etc., have become an important part of our daily life and special missions. Most of these devices are powered by electrochemical batteries, which have limited energy capacity, need periodic replacement or recharging, and lead to environmental concerns. On the one hand, there is a huge amount of energy stored in the human body and the energy dissipation rate is more than 100 Watts, while on the other hand, the power requirement of typical wearable and mobile devices is less than 1 Watt. Extracting a small amount of energy from the human body can provide enough power for many wearable/mobile devices, and enable a convenient, sustainable, eco-friendly, and self-powered alternative to batteries. In this talk, we will first review the mechanism and performance of the state-of-the-art biomechanical energy harvesting devices in three categories in terms of excitation mechanisms, specifically, relative-motion-excited, inertia-excited, and force-excited. Then we will present our research in these three categories: including electromagnetic negative-muscle-work energy harvesters from the human ankle, backpack energy harvesting while enhancing the human comfortable, and piezoelectric footwear energy harvesters. The future research challenges and directions are also outlined.