Since two decades, we are observing a continuous evolution in wireless communications and networking technologies. This evolution creates nowadays an unprecedented demand for accessing communication services anywhere, anytime and using any device. This trend is also encouraging the rapid development of more and more novel communication services and applications. These latter require more capacity and more quality of service from the network, as well as more efficiency from the communication device. One of the main goals in current research is to design new communication solutions that are more robust and resource-efficient. In this context, our aim is to propose novel mechanisms and protocols that target the "improvement of the resource usage in wireless packet networks". Improving the resource usage can be realized at two complementary levels: the packet-level and the connection-level. In our research, we addressed and solved different facets of the resource usage issue at both levels. At the connection level, our main concern was to maintain the experienced quality of service while the users are willing to move transparently over the diverse available wireless packet networks; while at the packet-level the issue we addressed was to improve the quality of service experienced by the packet flows generated by novel data and multimedia communication services. This report presents the major research results we obtained in this field.