Cross-layer design (CLD) has emerged as an important area in wireless sensor networks (WSNs). Cross-layer enables interaction between different non-adjacent layers and, thereby, exchanging information between layers, which, indeed is not possible in traditional architectures. CLD is used for enhancing the performance of the existing architectures by utilizing the flexible prospects of the protocol layers to improve system performance and to satisfy QoS demands of the applications. The CLD leads to increase in network efficiency and optimized network throughput. In this paper, the various cross-layer design methodologies for WSNs have been reviewed, which have basically been designed to enhance the network performance in WSN. At the end, the paper proposes a CLD based on ongoing research.