Book excerpt: Heterogeneous wireless networking, which is sometimes referred to as the fourth-generation (4G) wireless, is a new frontier in the future wireless communications technology and there has been a growing interest on this topic among researchers and engineers in both academia and industry. This book will include a set of research and survey articles featuring the recent advances in theory and applications of heterogeneous wireless networking technology for the next generation (e.g., fourth generation) wireless communications systems. With the rapid growth in the number of wireless applications, services and devices, using a single wireless technology such as a second generation (2G) and third generation (3G) wireless system would not be efficient to deliver high speed data rate and quality-of-service (QoS) support to mobile users in a seamless way. Fourth generation (4G) wireless systems are devised with the vision of heterogeneity in which a mobile user/device will be able to connect to multiple wireless networks (e.g., WLAN, cellular, WMAN) simultaneously. This book intends to provide a unified view on the state-of-the-art of protocols and architectures for heterogeneous wireless networking. The contributed articles will cover both the theoretical concepts and system-level implementation issues related to design, analysis, and optimization of architectures and protocols for heterogeneous wireless access networks.