Aspergillus fumigatus is a filamentous fungal saprophyte that is ubiquitous in the environment. It is also a human pathogen and induces allergenic response, negatively impacting health care and associated costs significantly around the world. Much of the basic biology of this organism is only poorly understood, but the recent completion and publication of its genome sequence provides an excellent tool for researchers to gain insight into these processes. In this review we will summarize some of the more salient features revealed by analysis of the genome, including the search for candidate pathogenicity genes and the switch to a pathogenic lifestyle, allergen proteins, DNA repair, secondary metabolite gene clusters that produce compounds both useful and toxic, a theoretical capability of this asexual organism to reproduce sexually, signalling, and transcription. A. fumigatus was compared with the food biotechnology fungus Aspergillus oryzae and sexual fungus Aspergillus nidulans, as well as other fungi, in an attempt to discern key differences between these organisms.