The human torso includes three major segments, the thoracic (rib cage) segment, lumbar segment, and pelvic segment to which the thighs are attached. The JOHN model was developed to represent the positions and movements of these torso segments along with the head, arms, and legs. Using the JOHN model, a new seat concept has been developed to support and move with the torso segments and thighs. This paper describes the background of the biomechanically articulated chair (BAC) and the development of BAC prototypes. These BAC prototypes have been designed to move with and support the thighs, pelvis, and rib cage through a wide variety of recline angles and spinal curvatures. These motions have been evaluated with computer modeling and with initial experience of human subjects. Results from computer modeling and human subjects show that the BAC will allow a broad range of torso postures. In a BAC, people can choose between two basic modes of operation: 1. the articulations of the BAC can will follow and support their selections of torso posture, or 2. the components of the BAC can be positioned and the user's posture will respond to the positions of the BAC. The BAC prototypes demonstrate that seats can be designed which allow and support a broad range of seating postures and that seats can move with people as they change their posture.