The Authors report the milestones which led to the discovery of the mite Dermatophagoides pteronyssinus as the main allergen source in house dust, and discuss its etiological role in allergic respiratory diseases. The present knowledge on the importance of other species of mite potentially allergenic in man is focused. From a biological point of view, the taxonomy, anatomy and physiology of these important Arthropods are described. Furthermore, the techniques for the collection and identification of mite specimens in house dust samples are briefly described. From an ecological point of view, the most important factors which regulate the peculiar distribution of some mite species in the domestic and occupational environments (i.e. relative humidity of air, temperature, sources of food) are described. The Authors, furthermore, report the theoretical criteria and the practical procedures for the control of mite growth in the houses. The main physical, chemical and immunological characteristics of the mite allergens are described. The Authors emphasize the studies on cross-reactions between different mite species, from which the importance of the storage mites as allergens of clinical relevance appears clearly. Furthermore, the techniques for the diagnosis and immunotherapy of the mite-related allergic diseases are briefly described.