TWOWAY is a full six degree-of-freedom position measurement system which operates cooperatively between two relatively remote but independent bodies. TWOWAY functions symmetrically, employing a relatively simple electromagnetic signal which is alternately received from, processed and transmitted to the other body in a transponding or multiplexed fashion. The result is that TWOWAY can provide in each body a measure of: the two pointing angles and range which define the direction to and the position of the other body plus, the three Euler angles (or direction cosines) which define the relative orientation between the two bodies. TWOWAY consists of an antenna which is precisely fixed and oriented to its body; the signals received from and transmitted to the other body are processed by the System Electronics Unit (SEU). A suitable display or control interface is also required depending upon the application. In this paper, TWOWAY components and options are described; their function in TWOWAY operation is explained.