This article summarizes the EU's activities in the ACTS program on mobile satellite communication, which are directed to the satellite component of UMTS. In this article the projects INSURED, NEWTEST, SECOMS, SINUS, and TOMAS are briefly introduced, and their R&D work on the services implemented in the different test platforms, the network integration scenario into the UMTS network, the studies performed for the air interface, the mobile terminals implemented, and the demonstrated applications are summarized. Furthermore, a new approach using neural networks for adaptive channel equalization and the concept for an EHF/Ka-Band system are introduced.