Activated carbons are well known as efficient materials for the removal of difficult to degrade pollutants from water according to their excellent sorption capacity. This ability is related to their well-developed porous network. Activated carbons were traditionally prepared from lignite or coal but also wood and coconut shell. Over the past 20 years an extensive literature describes the preparation of activated carbons from naturally abundant and locally available renewable resources such as agricultural wastes (e.g. sugar cane bagasse, olive oil, coffee, rice, maize, nuts and shells) and also from sewage sludge. Activated carbon synthesis can be realised by two well-known processes: physical activation involving a carbonisation followed by an activation step with an oxidising gas; or chemical activation involving a single carbonisation step of the precursor in the presence of a chemical agent. Non-conventional methods such as microwave heating and hydrothermal carbonisation treatment are now being developed for activated carbon preparation and appear to be sustainable processes. The yield, textural characteristics and surface chemistry of the activated carbons are highly dependent on both the initial composition of the precursor and the preparation process. Textural and physico-chemical properties determine the adsorptive properties of activated carbons and their removal of pollutants such as dyes, chlorinated compounds and metals.