Among all biomass sources, the lignocellulosic biomass derived from agricultural and forestry wastes is considered as the most adequate substitute for fossil sources due to its abundance, versatility and lack of competition with food resources. Yet, the efficient and economically feasible conversion of lignin into fuels and chemicals remains one of the major technology gaps for the development of lignocellulosic biorefineries. Here, the chemical nature of the lignin biopolymers will be described based on their botanical origin and the isolation process. After summarizing the most relevant advances in the catalytic conversion of lignin, the recently developed Ligninto-Liquids (LtL) process will be described and its major challenges addressed. 1.1 Energy transition: from crude oil to a biomass based energy system According to the results of the 2015 Revision 1 published by the Department of Economic and Social Affairs of United Nations (UN-DESA), the world population reached 7.3 billion as of mid-2015. The global population is expected to rise in the short-to-medium term, reaching between 8.4 and 8.6 billion in 2030 and between 9.5 and 13.3 billion by the end of the century 1. Hence, the demand of natural resources for the production of food, energy and chemicals is expected to increase significantly in the course of the century. It is important, therefore, to develop an integrated production model that addresses the sustainable and environmentally friendly production and distribution of these three basic commodities: food, energy and raw materials (chemicals). The challenge is of immense magnitude. In terms of food supply, the Food and Agriculture Organization (FAO) expects an steady growth of the total agricultural product consumption of 1.1 % per year until 2050 2. The global energy demand is estimated to grow even faster, by 48 % between 2012 and 2040 (Figure 1.1, above); fossil fuels being the major contributor providing over 78 % of the demand 3. The same trend is observed for the bulk chemicals, of which organic chemicals account for 4 CHAPTER 1