This book focuses on the properties of deep eutectic solvents (DESs) and recent advances in their application in lignocellulosic biomass processing. Lignocellulosic biomass conversion to biofuels, biochemicals and other value-added products has attracted global attention because it is a readily available, inexpensive and renewable resource. However, in order for biomass technologies to be commercially viable, biomass recalcitrance needs to be cost-effectively reduced. Deep eutectic solvents (DESs) are new 'green' solvents that have the high potential for biomass processing thanks to their low cost, low toxicity, biodegradability, and easy recycling and reuse. After an overview of the current lignocellulosic biomass pretreatment, the book discusses the synthesis and physiochemical properties of DESs, as well as key findings on the effects of DES on cellulose, hemicellulose and lignin solubilization, biomass pretreatment and biomass crystallinity. It then addresses the enzymatic hydrolysis performance of DES-pretreated solids, compatibility of DESs with enzymes and microorganisms, and the recycling potential of DESs. Lastly, it compares DESs with ionic liquids, and examines the challenges and opportunities relating to extending the use of DESs in lignocellulosic processing.