During the entire era of space flight air launch is seen as a very promising concept. Despite its claimed advantages, air launch is up till now only a marginal success with the Pegasus launch vehicle from Orbital Sciences. In this study is investigated for which conditions expendable air launched vehicles can achieve a performance gain compared with expendable ground launched vehicles. The scope of this study is limited to near-term feasible concepts. Therefore, only existing carrier aircraft that require minimum modifications are evaluated. Solid propelled rockets are more promising for air launch than liquid rockets, therefore, only solid propelled rockets are considered during this study. Potential markets for launch vehicles with a 10 kg and 2,000 kg payload capability to low earth orbit are identified. The influences of different launch parameters and the presence of a wing on the potential performance gain of air launch are investigated. A Multidisciplinary Design Optimization (MDO) is deemed the most suitable approach for the comparison between air launch and ground launch. In earlier thesis work performed at the TU Delft a MDO tool in the Tudat framework is developed by Jan Vandamme. This tool is used as a starting point for this work but is heavily modified and expanded. Air launch can provide a reduction in the cost per flight between 26.9 and 31.3%. For a payload of 10 kg the gross take-off weight of the launch vehicle can be reduced with 66.7-70.1% while this is 33.6-47.4% for the 2,000 kg payload class vehicles. Moreover, air launch reduces the amount of ?V required to orbit with between 935 and 1,225 m/s compared to ground launch for a 10 kg payload for subsonic launch conditions. The ?V advantage of air launch for the 2,000 kg payload class is between 302 and 797 m/s. Winged vehicles provide a small cost advantage (2.45%) compared to wingless vehicles for horizontal launch as well as an advantage for the GTOW (19.9%) and the required amount of ?V to orbit (4.60%). As soon as a winged launch vehicle will be released under a positive flight path angle the cost advantage and the ?V advantage of the winged configuration will diminish quickly.