Bioaerosols such as bacterial and fungal cells and their spores are - along with non-biological particles - part of indoor airborne particulate matter and have been related since a long time to health issues of human beings as well as flora, and fauna. To identify the different risks and to establish exposure thresholds, microbiology of air samples from a series of indoor environments must be characterized, i.e. the different microorganisms (bacteria and fungi) must be identified and quantified. This review discusses the techniques of air sampling and sample analysis. In addition, a literature study has been performed regarding the levels of these microorganisms in various indoor occupational (e.g., schools, offices, hospitals, museums) and dwelling environments. These results will provide a significant scientific basis for indoor air quality control and help in elaborating risk prevention programs for workers and dwellers. This review shall contribute to the knowledge of identification and quantification of airborne microbial constituents in various indoor environments. Combining the indoor microbial load data with data from studies focusing on health effects caused by inhalation of specific airborne microorganisms will allow the evaluation of various risks to which inhabitants are exposed.