Phycology (from Greek φῦκος, phykos, "seaweed"; and -λογία, -logia) is the scientific study of algae. Also known as algology, phycology is a branch of life science and often is regarded as a subdiscipline of botany.

Algae are important as primary producers in aquatic ecosystems. Most algae are eukaryotic, photosynthetic organisms that live in a wet environment. They are distinguished from the higher plants by a lack of true roots, stems or leaves. They do not flower. Many species are single-celled and microscopic (including phytoplankton and other microalgae); many others are multicellular to one degree or another, some of these growing to large size (for example, seaweeds such as kelp and Sargassum).