a GMC-oxidoreductase (5–100 mM). The lower catalytic rate of Class I and Class II CDHs (below 50 s−1) compared to glucose oxidase (300–2000 s−1) is probably an evolutionary adaption to the acquired CYT domain to optimize IET and prevent futile reactions of the substrate in an idle active-site. CDH as a bioelectrocatalyst CDH exhibits various properties that makes it a suitable electrocatalyst for biosensors or biofuel cells. Unlike any other carbohydrate converting GMC-oxidoreductase it can be contacted via mediated electron transfer (MET) or direct electron transfer (DET). CDH-based 2nd and 3rd generation biosensors for the quantitation of commercially or medically relevant molecules such as glucose or lactose have been developed. The advantage 2nd generation biosensors is their high sensitivity, the advantage of 3rd generation biosensors is the avoidance of redox mediators in implantable blood glucose monitoring systems. CDH-based 3rd generation biosensors have a robust performance because of the good thermal and turnover stability of CDH and the mobile CYT domain, which can interact with many electrode materials and surface modifications and deliver reasonably high current densities. CDH-based biosensors CDH has been used as biosensor element for the detection of a number of different analytes ever since 1992, when Elmgren et al. reported on a new biosensor sensitive towards cello-oligosaccharides with degrees of polymerization of 2 to 6, lactose and maltose. Research on CDH employed as biosensor since then until 2013 has been reviewed, providing lists of CDH-based biosensors in both DET and MET mode for phenols (catechol, dopamine, noradrenaline, hydroquinone, aminophenol) and carbohydrates (cellobiose, lactose, maltose, glucose). Both Class I and Class II CDHs have been employed as biocatalysts for biosensors. In accordance with their preferred substrates, Class I CDHs were mainly applied for the detection and quantitation of phenols, cellobiose, and lactose, whereas Class II CDHs have been applied for the detection of cellobiose, lactose, maltose and glucose. Among Class I CDHs, Phanerochaete chrysosporium CDH is the most comprehensively studied enzyme was employed for the detection of various phenol derivates, cellobiose and lactose. Phanerochaete sordida and Trametes villosa CDH have been used for the detection of lactose and Sclerotium rolfsii CDH for the detection of dopamine. Among Class II CDHs, Crassicarpon hotsonii and Crassicarpon thermophilum CDH were employed as recognition element for cellobiose, lactose, glucose and maltose and Humicola insolens CDH for glucose and maltose. Detection of maltose was in all cases only reported to show that maltose is