Disease manifestations with Aspergillus spp. are very diverse and dependent on interaction between the fungus and the host. Invasive aspergillosis (IA) is the most severe form of Aspergillus - associated disease found in immunocompromised hosts. Infections are mainly due to Aspergillus (A.) fumigatus, an air-borne opportunistic pathogen that causes 90% of IA. Mortality rate of this disease is still very high (50-95%), partly because of diagnostic difficulties, limited antifungal treatment options, weak conditions of patients at risk; but also in part because understanding of virulence factors involved in A. fumigatus pathogenicity and interactions of the pathogen with the host immune system is still poor. This review focuses on properties of A. fumigatus in terms of putative virulence factors and interactions of the pathogen with a main focus on the innate immune system.