Hydrophobins are small proteins produced by filamentous fungi which assemble into amphipathic monolayers at hydrophobic:hydrophilic interfaces. They play a number of different functional roles, including reducing surface tension, facilitating attachment to surfaces and mediating fungal-host interactions. The genome of Aspergillus fumigatus encodes six different hydrophobins, RodA-RodF. RodA has been shown to form a protein monolayer on the surface of the conidia (Aimanianda et al. 2009). This layer shields the PAMPS within the cell wall from recognition by the host immune system. RodB is expressed in the mycelium when A. fumigatus is grown under aerial static conditions, such as those in vivo under conditions of invasive aspergillosis (Beauvais et al. 2007). RodA and RodB both form filamentous structures known as rodlets, which share many structural characteristics with amyloid fibrils. We have determined the monomeric structures of these two proteins and have carried out a program of mutagenesis to identify residues in the proteins which are critical for assembly into rodlets and formation of the amphipathic monolayers. A clear picture of the structure of the monomeric and polymeric forms of these hydrophobins will lead to an understanding of the specific functional roles played by the different hydrophobin proteins in A. fumigatus during normal growth and host infection.