Abstract: Time synchronization is one of the basic middle-wares of wireless sensor networks. Many time synchronization protocols which are based on exchanging packets with timing information have been proposed in recent years. However, in large scale wireless sensor networks, the accumulation of synchronization error over hop distance and the demand for scalability challenge these traditional time synchronization techniques. To deal with these two challenges, researchers from the field of wireless sensor networks are beginning to pay attention to the old technique of firefly-inspired synchrony and the new emerging cooperative synchronization technique. Great progress has been made in the technique of firefly-inspired synchrony in recent years, especially in single-hop network after the model of Strogatz and Mirollo was proposed. However, although a great number of experiments and simulations have been conducted, its characteristics of convergence in multi-hop network still needs to be found in theory. Based on the novel idea of spatial averaging instead of the traditional idea of time averaging, the technique of cooperative synchronization presents another new solution to time synchronization in wireless sensor networks although it is still strolling on simulation stage at present. Its basic idea and research and application status in wireless sensor networks are introduced. Future research directions are also proposed.