Mechatronics technologies are now steadily penetrating in our daily lives. We are surrounded by mechatronic products and interact with them in many ways. In particular, mechatronics devices may potentially improve the quality of life of elderly people and patients with impairments. In this talk, several key technologies that we have developed for assisting such people in walking are introduced. These technologies include sensing technologies for identifying the intent of human, decision making algorithms to decide the right amount of assistance to the human and actuation technologies to provide forces and torques to selected human joints. In the design of mechatronic devices interacting with humans, the dynamics of human is an important element and the compatibility between machine and human must be optimized. If the device is interacting with normal and healthy humans, the design may take advantages of robust and intelligent controllability of a human. In case of assistive devices fo...