Liquefied natural gas (LNG) has been the fastest increasing fossil fuel in the world energy market due to its low carbon dioxide emission, high energy density, and ease of transport. However, the liquefaction of natural gas is one of the most energy-intensive industrial processes. Thus, it is very important to design new liquefaction processes and optimize the existing ones in order to reduce the energy consumption. In this paper, we present a state-of-the-art review of the recent progress on the design and optimization of NG liquefaction processes for onshore and offshore applications. The current onshore processes include the cascade, mixed refrigerant, and expander-based processes, of which the mixed refrigerant process has received the most attention. The common objective function of the onshore LNG process optimization is the minimization of the energy consumption. However, for the offshore applications, the single mixed refrigerant and nitrogen expansion processes have been considered to be the promising options. For these, deck space and sensitivity to platform waving need be considered apart from energy consumption. Finally, we propose several potential developments for NG liquefaction process design and optimization. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.