This book provides significant knowledge on innovative radio resource management schemes for satellite communication systems that exploit lower layer adaptivity and the knowledge of layer 3 IP QoS support and transport layer behavior. This book is an interesting novelty since it integrates competencies considering all the parts of system design (i.e., propagation aspects, radio resource management, access protocols, network protocols, transport layer protocols, etc.) to cover both broadband and mobile satellite systems. A detailed analysis of cross-layer air interface design will be provided with new simulation results, proving that such approach can permit to guarantee high QoS levels for differentiated traffic classes and high utilization of air interface resources. Two scenarios will be addressed for cross-layer optimization issues, that is the satellite version of the terrestrial UMTS for mobile users (3GPP) and the DVB-S/-S2/-RCS air interface for broadband fixed transmissions (ETSI).