Technical Abstract: Char(coal), and a broader term black carbon (that includes soot) has long been recognized as a normal environmental (including soil) constituent resulting from fire and industrial activities. Biochar soil amendment has received global interests as a tool for carbon sequestration in conjunction with bioenergy production. In addition to the active research in both academic and federal sectors, biochar has received significant interests from policy makers and practitioners, partly because of easily understood concept and application. Most importantly, farmers can produce biochars themselves by slow pyrolysis of agricultural wastes on-farm. Despite its popularity and field trials already taking place around the globe, biochar can give mixed results for intended application, most importantly on the crop yield. This chapter will explore the benefits and potential risks of biochar soil amendment with a particular emphasis on the structural components of biochars. Selected characterization methods will be discussed, especially microscopic and spectroscopic techniques that are useful for understanding micro- to nm scale interactions and for addressing biochar aging, but have thus far been underutilized.