This book helps the readers get a holistic understanding of the emergence of biochar-nanocomposite research. The low and long-term exposure of persistent hazardous pollutants in environment is well known for damaging the water, soil, sediments, and living biota. Thus, it is a crucial step to eliminate these pollutants from environment regimes to prevent the on-site destruction or the transfer into the food chain. Biochar is a carbon-rich solid material generated through pyrolysis of biomass, and currently, it is covering the hotspot in environmental management of pollutants. It is being utilized for the efficient immobilization and sorption of organic pollutants, heavy metals, dyes, improvement of soil redox conditions, aggregate stabilization, photocatalytic degradation, and for carbon sequestration. The fascinating properties like surface area, porous structures, functional groups, and mineral components turn it into suitable candidate for the removal of various class of pollutants from environmental matrices. Different reactions like sorption, reduction, precipitation, solidification, and degradation are mainly responsible for the effective cleaning of xenobiotics from environment through biochar application. However, rapidly evolving contaminants in the environment have made the remediation more complex, expensive, and challenging. In view of these aspects, the modification of biochar through the doping of nanometals/metal oxides/surfactants/ or chemical entities will result in modified biochar with high surface area, more functional entities, improved physical, chemical, thermal, and mechanical characteristics with more adsorptive sites. Inclusion of these exclusive properties can be done through magnetic modification, impregnation of nanometals/ metal oxides/surfactants, amination, acid/base reactions, steam activation, etc. The resulted biochar-based nanocomposites have demonstrated a vital role in remediation of persistent organic pollutants, radionuclei, and heavy metals through the various interaction mechanisms like surface complexation, π-π interaction, electrostatic interaction, hydrogen bonding, Fenton process, and photocatalytic degradation. Currently, advanced research work has been carried out for the designing of modified composites of biochar to achieve maximum removal efficiency, reusability, biotoxicity, and sustainability. Hence, for selective removal of pollutants through designed biochar surface with the focused experimentation toward optimization of feedstocks, process variables, appropriate impregnation of nanomaterials, interaction with secondary pollutants, physical environment, longevity, and regeneration will definitely pave the way for safe and commercial application of biochar-based nanocomposites.