Pollen is a powdery substance produced by flowers of seed plants. It is a mass of microspores that appears as a fine dust and varies greatly in shape and structure. Pollen grains have a hard outer wall made of sporopollenin, which is highly resistant to environmental damage and may even survive in sedimentary rocks for many millions of years. The outer wall of the pollen grain is often elaborately decorated and may be punctuated with small openings called apertures. Pollen is used for transferring haploid male genetic material from the anther of a single flower to the stigma of another in cross-pollination. Pollen is infrequently used as food and food supplement, but it is often contaminated by agricultural pesticides.

Pollen is a common trigger of seasonal allergies, and one in five Australians suffer from hayfever caused by pollen. Pollen is a fine yellowish powder that is transported from plant to plant by the wind, by birds, by insects, or by other animals. The spread of pollen helps to fertilize plants and can mean misery for seasonal allergy sufferers. Pollen can cause symptoms such as sneezing, nasal congestion, runny nose, watery eyes, itchy throat, and eyes, and wheezing. Pollen can also aggravate asthma symptoms, including increased coughing and wheezing.

The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archaeology, and forensics. Pollen grains are very common constituents of geologic sediments, both recent and ancient, and have provided much information on the origin and geologic history of terrestrial plant life. Nearly all angiosperm and gymnosperm plant families and many genera can be identified solely by their pollen grains.