**Abstract**

The chapter focuses on recent trends of biomass conversion into valuable energy, chemicals, gaseous and liquid fuels. Biomass is presently the largest source of renewable energy and the primary bioenergy resource in the world. A comprehensive discussion on different types, sources and compositions of biomass is presented. The most abundant biomass on the earth is lignocellulose and it represents a major carbon source for chemical compounds and biofuels. The chapter presents a thorough review of lignocellulosic biomass and the importance of biomass as a renewable source. It then reviews biomass classification and composition. It introduces the analysis of biomass feedstock. Biomass is converted to energy, chemicals and clean fuels using various conversion techniques such as thermochemical, chemical and biochemical. The chapter provides a thorough examination of thermochemical conversion processes that use high temperatures to break down the bonds of organic matter. It briefly introduces combustion and gasification, followed by a comprehensive review of different pyrolysis techniques.

**Keywords:** bioenergy, hydrothermal processing, lignocellulosic biomass, biomass composition, pyrolysis, gasification, combustion
