The next-generation wireless networks such as the fourth generation (4G) cellular systems are targeted at supporting various applications such as voice, data, and multimedia over packetswitched networks. Providing quality of service (QoS) guarantees for these applications is an important objective in the design of the next-generation wireless networks. In this paper, we overview the issues and techniques in QoS provisioning for wireless networks, and present some of our recent results in this area. Specifically, we survey the results in five sub-areas, namely, network services models, traffic specification, packet scheduling for wireless transmission, call admission control in wireless networks, and wireless channel characterization. For each sub-area, we address the particular issues, review major approaches and mechanisms, and discuss the trade-offs of the approaches.