Exhaled breath condensate (EBC) is a promising source of biomarkers of lung disease. EBC is not a biomarker, but rather a matrix in which biomarkers may be identified, in that way equivalent to blood, sweat, tears, urine, and saliva. EBC may be thought of either as a body fluid or as a condensate of exhaled gas. The field of EBC research has advanced gradually, with the debates surrounding an emerging field helping to pose questions and gradually leading to answers. Conscientious assay technique will likely find in EBC any substance of substantially high enough concentration in the airway lining fluid.