Next generation 5G networks will support not only emerging services, but also other services which may be beyond our imagination today. Improving the system capacity remains nevertheless one of the most important targets of 5G. Long Term Evolution (LTE) operation over the unlicensed band (U-LTE) is considered as one promising solution to achieve this target. In this chapter, we introduce the state of the art coexistence technologies of U-LTE with other unlicensed systems. Specifically, we investigate the coexistence of LTE Licensed Assisted Access (LAA; LAA is the preferred mode of operation for U-LTE and was newly released in 2015) with Wi-Fi over the unlicensed band. To this end, we first develop an analytical model to study the performance of the existing Load Based Equipment (LBE) MAC for LAA, identify the fairness issues, and quantify the reservation overhead of the protocol. Next, we propose a hybrid MAC protocol for LAA to maximize the network throughput, by minimizing LAA MAC reservation overhead while ensuring fair spectrum sharing of U-LTE and Wi-Fi. To achieve the best coexistence performance, a two-level renewal process-based model is developed to analyze the proposed MAC and optimize its parameters. Extensive simulations using NS-3 are conducted to validate the analysis and demonstrate the efficiency of the proposed MAC protocol.