When organic materials (woody or agricultural materials, organic residues, sewage sludge, digestate,…) are thermally decomposed in the absence of oxygen, one of the resulting products is bio-char, a solid compound rich in carbon and inorganic elements. Incorporated into the ground, bio-char is a porous soil enhancer that can lock up carbon, supply minerals, prevent nutrient leaching and water contamination and retain soil moisture. As a result, bio-char can be an efficient material to enhance soil properties while sequestering carbon. However, bio-char’s porous properties make it also suitable for a variety of value-added applications: adsorption of pollutants, filler for composites, catalysts, material for electronic applications, etc. Bio-char properties depend on the biomass feedstock used as well as the operating conditions used for its production. Moreover, these properties can be manipulated by pre- and post-processing. By understanding and controlling these factors, it is possible to create value-added “designer biochars” for specific applications.