Research on Multicast Routing Techniques in Wireless Sensor Networks (WSNs) focuses on efficiently transmitting data from one source node to multiple destination nodes while minimizing energy consumption and communication overhead. Recent advancements emphasize energy-aware multicast tree construction, where nodes are selected based on residual energy and link stability to prolong network lifetime. Bio-inspired algorithms such as ant colony and particle swarm optimization are widely applied to enhance path selection and load balancing. QoS-aware multicast protocols integrate latency, reliability, and bandwidth considerations to ensure consistent data delivery in real-time applications. Emerging studies also explore 6LoWPAN-based multicast routing, virtual backbone formation, and network coding techniques to improve scalability and fault tolerance. Overall, multicast routing continues to evolve toward adaptive, intelligent, and energy-efficient frameworks suitable for large-scale and heterogeneous WSN environments.