This paper describes the successful research and development (R&D) of parallel bicycles (PB robots) including six prototypes created by the authors and their applications to personal vehicles. The first, developed in 1986, consists of a pair of coaxial wheels and an inverted pendulum on the wheel axis. Since then, the authors have carried out fundamental and practical studies on static/dynamic posture stabilization control, dynamic movement, and slope and stair ascent/descent. The PB robot control mechanism has recently been applied to educational robots, mobile humanoid robots, and personal vehicles. This paper also discusses personal vehicles commercialized as an application of the PB robots.