Filamentous fungi (moulds) are ubiquitous soil inhabitants whose conidia are inhaled into the respiratory tract, where they may cause life-threatening infections. Among these infections is invasive aspergillosis, which is a major cause of morbidity and mortality in the severely immunocompromised. Risk factors for invasive aspergillosis include prolonged and severe neutropenia, hematopoietic stem cell and solid organ transplantation, advanced AIDS, and chronic granulomatous disease. Invasive aspergillosis most commonly involves the sinopulmonary tract reflecting inhalation as the principal portal of entry. Chest computed tomography scans and new non-culture-based assays such as antigen detection and polymerase chain reaction may facilitate the early diagnosis of invasive aspergillosis, but have limitations. Reflecting an important unmet need, there has been a significant expansion in the antifungal armamentarium. The second-generation triazole, voriconazole, was superior to conventional amphotericin B as primary therapy for invasive aspergillosis, and is the new standard of care for this infection. There is significant interest in combination antifungal therapy pairing an echinocandin with either an azole or amphotericin B formulation as therapy for invasive aspergillosis. In addition, there has been an increased understanding of the immunology of Aspergillus infection, paving the way to novel immune augmentation strategies in animal models that merit evaluation in phase I clinic trials.