Mobile Optical Free-Space Communication (MFSO) downlinks from observation platforms in low earth orbit or in the atmosphere will allow nearly undetectable high-speed data links with small and low-power laser communication terminals. Several research institutions and companies are developing MFSO terminal technology for application in tactical and strategic communication scenarios as well as for civilian and security purposes. DLR is advancing this technology based on mature terrestrial fiber link components towards reliable and cost-effective free-space links. Successful demonstrations in the lower troposphere, the stratosphere, and from space have shown the potential of this technology. Future applications of MFSO will cover high-speed space downlinks, frequency distribution for navigation purposes, secure quantum key distribution, bidirectional links between aeronautic nodes, as well as near ground links between vehicles or ships. In this paper we will present aspects of the system design, calculate link performance limits, and show results of aeronautic and space downlink trials.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.