Quality of Service (QoS) in the Internet of Things (IoT) is a vital research area that ensures reliable, efficient, and scalable communication across heterogeneous devices and networks. Research papers in this field focus on addressing challenges such as latency, bandwidth utilization, energy efficiency, throughput, and packet loss, which directly impact the performance of IoT applications. Key studies propose QoS-aware routing protocols, resource allocation frameworks, priority-based scheduling, and cross-layer optimization techniques to meet the diverse requirements of smart healthcare, industrial IoT, intelligent transportation, and smart city ecosystems. Recent works also explore AI-driven QoS prediction, fog/edge-assisted decision-making, and blockchain-enabled service guarantees, while 5G/6G integration plays a crucial role in enabling ultra-reliable low-latency communication (URLLC) for mission-critical IoT services. By tackling interoperability, scalability, and dynamic traffic management, QoS research in IoT continues to enhance the reliability and user experience of next-generation connected environments.