<p>Biochar colloids, originating from fine fractions produced during pyrolysis or generated through post-application weathering in soils, exhibit distinct physicochemical properties that influence their environmental behavior. This review synthesizes research since 2010 on the formation mechanisms, stability controls, and mobility pathways of biochar colloids in soil environments, with emphasis on contrasting scientific viewpoints. Formation is driven by initial production of nano-scale particles and subsequent physical, chemical, and biological fragmentation. Stability depends on factors such as surface charge, ionic strength, cation valence, natural organic matter interactions, and heteroaggregation with soil minerals, with pyrolysis conditions and aging altering colloid reactivity. Mobility studies reveal that under favorable conditions, biochar colloids can travel through soil profiles or in runoff, potentially transporting sorbed contaminants or nutrients. This dual role underpins a central controversy: while biochar colloids can immobilize pollutants and enhance nutrient retention in situ, their mobility may facilitate contaminant migration and carbon loss. Field evidence suggests limited vertical leaching in many soils but significant lateral transport under high-flow or erosive events. The review evaluates the implications for carbon sequestration, water quality, and contaminant fate, highlighting both potential benefits and risks. Research gaps include long-term quantification of colloid export, fate in aquatic systems, and subtle ecological effects. Understanding the colloidal dimension of biochar behavior (i.e., the formation, stability, and mobility of its colloidal fraction) is essential for optimizing the&#xa0;<i>overall application</i>&#xa0;and environmental management of biochar in agriculture and remediation while mitigating unintended environmental impacts.</p>