Biofiltration is a low-cost, robust mitigation technology applicable to various agricultural emissions. Biofilters are essentially a pile of wood chips, mulch, compost or other porous, typically organic, media and its resident microorganisms used as an air ‘filter’. As contaminated air is forced through the biofilter media, the resident microbes breakdown the contaminants, cleaning the air stream. Though complex microbial interactions underpin biofilter function, adequate media quality, media moisture content, and residence time (length of time the contaminated air is in contact with the media) can ensure effective microbial communities development and biofiltration. Since the 1990’s, well-managed, farmer-constructed biofilters have been used with success to remove odor and other gaseous contaminants from livestock barn and manure treatment systems exhausts.