The ubiquitous fungus Aspergillus is capable of causing a wide spectrum of bronchopulmonary disease. It can behave as an allergen (causing asthma, hypersensitivity pneumonitis and allergic bronchopulmonary aspergillosis), as a commensal (leading to the formation of Aspergillomas), or as a pathogen (resulting in chronic cavitary aspergillosis, necrotising bronchitis or angio-invasive aspergillosis). This chapter explores the multifarious presentations of Aspergillus disease and contextualises them against the pathobiology of the fungus. The chapter also discusses the utility of the criteria used for the diagnosis of allergic bronchopulmonary aspergillosis (ABPA) and examines their rationale. It also includes a discussion of the various patterns of imaging related to the various forms of disease and the factors that need to be considered against the background of each. Also reviewed are the significance of ABPA-S as against ABPA-CB, and the surveillance strategies that may be adopted for early diagnosis of ABPA exacerbations. A discussion on the applicability and other details of galactomannan and beta-D glucan testing is also included.