From medical, especially clinical point of view, it is important to know the details about the occurrence of the pollen and spore load in the atmosphere. The flowering time of higher plants are events that come periodically in each season, but the time of blooming may differ from year to year, in different geographic locations. Based on differences recorded in several years of observations in airborne pollen, pollen calendars are drawn as an essential tool to allergy diagnosis and management. Allergic diseases such as bronchial asthma, allergic rhinitis and atopic dermatitis are dramatically increasing all over the world including developing countries. Today, more than 30% of the population is known to suffer from one or other allergic ailment. Major causative agents implicated are pollen grains, fungal spores, dust mites, insect debris, animal epithelia, etc. Several aerobiological studies have been conducted in different parts of the world to ascertain aerial concentration and seasonality of pollen grains and fungi. In India, first atmospheric survey was initiated in Calcutta in 1873 by Cunningham. Since then, researchers, all over India have conducted exhaustive studies on airborne pollen types and their concentration. An “All India Coordinated Project on Aeroallergens and Human Health” sponsored by the Ministry of Environment and Forests, Govt. of India, was successfully completed by the author and his colleagues to enlist national data base on atmospheric pollen and spores. Important pollen and fungal allergens from 18 different places were identified, quantified and characterized for their allergenic properties. This and work done by other workers provide the most scientific and up-to-date information on aeroallergens of India. The most prevalent pollen allergens are Amaranthus, Cynodon, Poaceae, Artemisia, Parthenium, Holoptelia, Prosopis, Morus, Eucalyptus, Ricinus, Cannabis and some others .