This paper presents an overview of advanced space propulsion concepts and their research activities at the beginning of the 21 st Century. If successfully developed, these concepts will enable in the coming decades the implementation of propulsion technologies that will reduce the cost of access to space and/or enable aggressive exploration, and ultimately exploitation of the Solar System and beyond. This paper focuses primarily on mid-to far-term in-space propulsion applications, although advanced launch concepts (e.g., launch assist catapults) are also discussed briefly.Examples of advanced propulsion concepts to be discussed include advanced chemical propulsion (high-energy density materials, gelled propellants, etc.), nuclear propulsion (fission, fusion, and antimatter annihilation), electric propulsion (solar-and nuclearelectric propulsion power systems and electric propulsion thrusters), micropropulsion, beamed-energy propulsion (e.g., solar/laser/microwave thermal/electric combinations), beamed-momentum propulsion (e.g., solar/laser/microwave sails, electromagnetic/plasma sails), aero/gravity assist, launch assist catapults, tethers (momentum exchange and electrodynamic), extraterrestrial resource utilization, and breakthrough physics propulsion.