Pollen grains only represent a small fraction of the total amount of the viable biological particles present in the air, but pollen are the most important aeroallergens in the outdoor environment. The analysis of pollen has traditionally been carried out by microscopy, which can be traced back to the 17th century. Modern advances in molecular analysis could improve information for allergy sufferers and health care professionals. Pollen allergy (pollinosis) was first described in the 19th century. The prevalence of respiratory diseases increased dramatically during the latter part of the 20th century and millions of individuals are now affected. A number of scientists devised equipment to examine airborne biological particles during the 19th century, but aerobiological monitoring only became standardized during the 20th century. Airborne pollen are routinely monitored in many parts of the world, such as North America and Europe, and the first limited network has also been created for monitoring airborne allergen concentrations. Monitoring of the environment is often based on a combination of measurements and model results. Source-based models can increase our knowledge of airborne pollen because they can explain situations and processes that are almost impossible to understand using observations alone.