This review highlights the occurrence and functions of mannans in plant materials, as well as enzymatic hydrolysis and microbial biodegradation thereof. Fungal 1,4-beta-D-mannan mannohydrolases (beta-mannanases) are discussed with regards to their mode of action with reference to auxiliary enzymes involved in the hydrolysis of mannans such as alpha-galactosidases, beta-mannosidases, beta-glucosidases and acetyl mannan esterases. The diversity and production of beta-mannanases by various species of the phyla Basidiomycota and Ascomycota are also highlighted. Cloning and heterologous expression of both fungal and bacterial beta-mannanases in fungal expression systems are reviewed, indicating production of enzymes at levels up to grams per litre and with high purity, making these production systems ideal for industrial enzyme production. Application of fungal beta-mannanases in the production of nutraceuticals, food and feed, and commodity products is discussed. (C) 2010 Elsevier Ltd. All rights reserved.