Guano (from the Quechua 'wanu') is the name given to the collected droppings of seabirds and bats. It can be used as an effective fertilizer due to its high levels of nitrogen. Soil that is deficient in organic matter can be made much more productive by addition of this manure. Guano consists of ammonia, along with uric, phosphoric, oxalic, and carbonic acids, as well as some earth salts and impurities. The high concentration of nitrates also made guano an important strategic commodity.

Guano is harvested on various islands in the Pacific (for example the Chincha Islands and Nauru) and in other oceans (for example Juan de Nova Island). These islands have been home to mass seabird colonies for many centuries, and the guano has collected to a depth of many metres.

Guano has been harvested over several centuries along the coast of Peru, where islands and rocky shores have been sheltered from humans and predators and administered by private and state companies. The Guanay cormorant has historically been the most important producer of guano; its guano also tends to be more rich in nitrogen than guano from other seabirds. Other important guano producing species off the coast of Peru are the Peruvian Pelican and the Peruvian booby .

See also: Guano Islands Act