Lignocellulosic biomass has been used as starting materials in the process of producing biofuels and chemicals. A pretreatment step is necessary to mitigate the inherent recalcitrance of lignocellulosic biomass during biochemical conversion. Certain ionic liquids (ILs) have been proven to be effective solvents to deconstruct recalcitrant lignocellulosic biomass for high sugar yield for over a decade. Dialkylimidazolium-based, choline-based, and protic acidic ILs are frequently used in biomass pretreatment. Extensive research in this field has been done with technological hurdles revealed during the process. In this review paper, advances in the biocompatibility of ILs and process integration, optimization and scale-up of IL pretreatment processes, IL recovery and reuse, and economic and sustainability analysis were presented. ILs continue to be actively used in biomass pretreatment due to their structural variability and functional tunability.