Mycolic acids (MAs) are the hallmark of the cell envelope of Mycobacterium tuberculosis and related species and genera. MAs are unique and complex molecular structures that are found either unbound, extractable with specific organic solvents such as esters of trehalose or glycerol, or esterifying the terminal pentaarabinofuranosyl units of arabinogalactan (AG), the polysaccharide that forms the insoluble cell wall skeleton together with peptidoglycan.