Resumen: Agricultural lignocellulosic waste can generate serious environmental problems if not properly managed. Biodegradation, through anaerobic digestion (AD), is a cost-effective strategy for biogas production. However, studies on the biodegradation of lignocellulose show that the substrate is recalcitrant to microbiological hydrolysis, which reduces the efficiency of converting organic matter into biogas. The main reasons are its complex structure and slow biodegradation. The appropriate performance of biomethanization suggests a deep knowledge of substrate composition. Typically, the composition is about 10% to 25% lignin, 20% to 30% hemicellulose, and 40% to 50% cellulose. This book chapter will summarize the AD process and rate-limiting steps, compositional properties (focusing especially on pretreatment strategies applied to lignocellulosic biomass to improve methane yield), and overall AD performance. The most common pretreatments applied to organic substrates will be studied: physical, chemical, biological, and a combination of them. Additionally, the new trends in pretreatments will be exposed.