Wearable and mobile devices are an important part of our daily life. Most of those devices are powered by batteries. The limited life span of batteries constitutes a limitation, especially in a multiple-day expedition, where electrical power can not access conveniently. At the same time, there is a huge amount of energy stored in the human body. While walking, there is a large amount of power dissipated in the human body as negative muscle work and the energy loss by impact. By sourcing locally and using locally, human body energy harvesting is a promising solution. This dissertation focuses on harvesting energy from the human body to power wearable and mobile devices while poses a minimum burden on the human body. Three topics related to the human body energy harvesting are explored, i.e, energy harvesting backpack, negative muscle work harvester, and energy harvesting tile/paver. The energy harvesting backpack was invented in 2006. Extensive work was done to improve the performance of backpack energy harvester. The backpack is modeled as a spring-mass-damper system. Mechanical Motion Rectifier was added to the springmass-damper system to increase the frequency bandwidth. A spring is added to the spring-mass-damper system, between the harvester and the backpack mass, and a inerter-based 2DOF (degree-of-freedom) backpack is created. The inerter-based 2DOF backpack improves the power output, frequency bandwidth, and power stroke ratio performance. MMR was added to the inerter-based 2DOF backpack to reduce the peak stroke. Compared with the conventional spring-mass-damper backpack, the MMR and inerter-based 2DOF backpack can harvest more power with large bandwidth at a small sacrifice of stroke. The electric damping was also tuned to increase the power output and bandwidth for the energy harvesting backpack. The negative work harvester mounts on the human ankle and harvests energy in the terminal stance phase in human walking, when the calf muscle is doing negative muscle work. This harvester is an analogy to regenerative brake in vehicles. The energy harvesting paver/tile harvests energy when the heel contacts with ground and energy are dissipated by impact.