Indoor air is a dominant exposure for humans. More than half of what a person gets into his body, during lifetime, is air inhaled in the home. Most illnesses are associated with exposures in indoor environments. Indoor air was, also, believed to be a major environmental factor for more than a hundred years, from the start of the hygienic revolution, around 1850, until outdoor environmental issues entered the scene and became dominant, around 1960. Today one or two magnitudes more funding of research goes to outdoor air-health, compared to indoor air-health. The main environmental issues today concern outdoor air quality, energy use, and sustainable buildings, but not IAQ/health! Today there is mounting evidence that indoor air quality is important for many illnesses, including allergies, other hypersensitivity reactions, airways infections, and lung cancer. Most of these illnesses are associated with "dampness", a low ventilation rate, and outgassing from furnishings, consumer products, etc. Still, we do not know about the role of, e.g. moulds. In the future much more emphasis must be on IAQ-health issues, from the perspectives of both public health and the national economy. The presentation will focus on the history of IAQ/health as well as on the present state of the art.