Biochemical conversion of biomass into biofuels, biochemicals, and biopolymers has attracted much interest throughout the world in terms of biorefineries. Lignocellulosic biomass is one of the most plentifully available biomass resources on the earth. It is composed of three main biopolymers - cellulose, hemicelluloses, and lignin, all of which are cross-linked to each other to resist degradation by enzymes and microorganisms resulting in so-called biomass recalcitrance. The biorefinery process typically consists of three steps: pretreatment, hydrolysis, and fermentation. Energy and cost efficiency of biorefinery is predominantly dependent on how to produce inexpensive sugars from complex cell wall component of lignocellulosic biomass by overcoming biomass recalcitrance. There have been tremendous efforts to develop effective biomass pretreatment technologies for obtaining the highest yield of fermentable sugars from biomass feedstocks at the lowest cost. The present review discusses various pretreatment technologies to understand how to effectively break down biomass into fermentable sugars that are eventually used for microbial fermentation to produce biomass-based fuels, chemicals, and polymers.