Hydrophobins are small amphipathic molecules found uniquely in fungi. They perform crucial roles in allowing filamentous species to break through interfaces during aerial hyphae formation, sporulation, fruit body production and cell penetration. Initial biotechnological applications have exploited materials coated with hydrophobins to switch hydrophobic surfaces to hydrophilic and vice versa. Recent improvements in our understanding of the biophysics of hydrophobin layer formation, including the use of mixed types of molecules, together with advances in genomics promise to extend greatly the potential for hydrophobin biotechnologies.