Lignocellulosic biomass, primarily composed of cellulose, hemicellulose, and lignin, is the most abundant renewable organic resource on Earth and holds tremendous promise as a feedstock for biofuels, biochemicals, and biomaterials. Its utilization not only reduces reliance on fossil fuels but also contributes to climate change mitigation and rural economic development. Despite the potential, its structural complexity and recalcitrance present significant challenges to efficient bioconversion. The rigid lignin–carbohydrate matrix limits enzyme accessibility and often requires energy-intensive processing. Pretreatment is therefore a vital step in biorefinery workflows, aimed at disrupting the biomass structure, enhancing enzymatic hydrolysis, and facilitating downstream processing. Various pretreatment strategies, including physical, chemical, physicochemical, and biological methods, offer different advantages and limitations in terms of efficiency, cost, environmental impact, and scalability. Recent innovations focus on integrating pretreatment into sustainable biorefinery frameworks, optimizing inhibitor formation, and adapting processes for diverse feedstocks. This chapter focuses on the principles, mechanisms, and recent developments in lignocellulosic biomass pretreatment technologies to aid in the selection and optimization of strategies for specific biomass types and processing goals.