<![CDATA[Biochar has evolved from a biomass carbonization product into an engineered material platform for carbon storage, energy, remediation, agriculture, and composite applications. However, recent literature remains fragmented across sectors, leaving the relationships among feedstocks, conversion conditions, structure, function, and sustainability impacts insufficiently understood. This review synthesizes the bibliographic records and abstracts provided in the reference dataset through title- and DOI-based deduplication, thematic relevance screening, and a comparative analysis of studies published over the past five years. The analysis is structured around a feedstock–process–structure–function–impact framework. The results show that temperature, residence time, atmosphere, heating rate, and activation govern the trade-offs among carbon yield, aromatization, surface functional groups, porosity, reactivity, and process emissions. Unmodified biochar is adequate for certain fuel and soil amendment applications, whereas pollutant and carbon dioxide capture, catalysis, energy storage, and composite reinforcement generally require surface engineering or hybrid architectures. Field evidence indicates that the optimum application rate is nonlinear and depends on the specific biochar–soil–plant combination; increasing the application rate does not necessarily produce greater benefits. In water treatment, laboratory adsorption capacity alone is insufficient to demonstrate feasibility because regeneration, leaching, ion competition, reactor configuration, and cost determine actual performance. This review proposes an intended-use-based biochar quality passport, tiered testing from the material to the system level, and life-cycle assessment that accounts for the product’s end-of-life fate. The novelty of this synthesis lies in integrating applications that are commonly examined separately and establishing a decision-making framework for matching biochar properties with their intended functions, risks, and implementation scales. This approach helps prevent universal claims and directs research toward long-term demonstration, standardization, and industrial integration that can be verified technically, economically, and environmentally across different regions.]]>
