Aspergillus fumigatus is the most significant airborne human-pathogenic fungus capable of causing infections and allergies in humans. Diseases associated with A. fumigatus are initiated by inhalation of its conidia. Surface proteins on these conidia can mediate direct contact with host immune system, facilitate adhesion to host cells, but also shield conidia from phagosomal elimination. Conidia, germlings, and outgrowing hyphae not only damage host cells and tissues, resulting in infections, but also expose and release antigens that provoke allergic reactions. Despite the identification of nearly two thousand surface-exposed or secreted proteins through bioinformatics and/or proteomics studies, only a few of these proteins have been functionally evaluated for their roles in pathogenesis. In this chapter, we will provide a summary of the current findings regarding A. fumigatus extracellular proteins and for their contributions to the development of diseases.