Book excerpt: Cross-layer design and optimization is a new technique which can be used to design and improve the performance in both wireless and wireline networks. The central idea of cross-layer design is to optimize the control and exchange of information over two or more layers to achieve significant performance improvements by exploiting the interaction between various protocol layers. Designing for wireless networks such as cellular networks, WLANs, mobile ad hoc networks (MANETs) and Wireless Sensor Networks (WSNs), poses more stringent requirements than wireline networks and are considerably different in their applications and architectures, although all use wireless channel for communication. Promising results achieved by cross-layer optimizations initiated significant research activity in this area. Due to features such as ease of deployment, increased coverage and enhanced capacity, multi hop wireless networks like ad hoc networks, and mixed network that form the network in a self-organized manner without relying on fixed infrastructure is touted as the new frontier of wireless networking. This work aims to review the present study on the cross-layer paradigm for QoS support in multi-hop wireless networks. Several examples of evolutionary and revolutionary cross-layer approaches are presented in detail. The Cross-Talk architecture represents one of the more aggressive approaches to cross layer improvement. This architecture enables performance related decisions at the global level that can propagate down to the local layer. This architecture fits the Mixed Network modeling developed here at MSU for the iNET project. Organizing the Mixed Networks solutions into the framework of the Cross-Talk Architecture will allow this work to build on the body of research already in place for cross layering.-- Abstract.