Tethers have been studied and validated in space since the 1960’s, and many studies show their applicability across a broad range of applications, including space propulsion, power generation, formation flying, multi-point ionospheric science, and active space debris removal. Important milestones include retrieval of a tether in space (Tethered Satellite System 1992), successful deployment of a >30-km tether in space (Young Engineer’s Satellite 2, 2007), operation of an electrodynamic tether with tether current driven in both directions-power and thrust modes (Plasma Motor Generator 1993), high tether current capability (Tethered Satellite System Reflight 1996), demonstration of a long-term (∼10 year) tether operation on-orbit (Tether Physics and Survivability Experiment 1996-2006), and the successful deployment of a tape tether (Japan Tether Experiment 2010). Various types of tethers and systems could be used for space applications. Electrodynamic tethers can use solar power to ‘push’ against a planetary magnetic field to achieve propulsion without the expenditure of propellant. Utilizing completely different physical principles, long non-conducting tethers can exchange momentum between two masses in orbit to place one body into a higher orbit or a transfer orbit for lunar and planetary missions. Tethers can also be used to support space science by providing a mechanism for precision formation flying, fixe baseline multi-point science observations, and for reaching regions of the upper atmosphere that were previously inaccessible.