The large field of flow visualization is briefly reviewed. Definition, purpose, and classification into subfields are outlined, and the reader is directed toward more detailed and more specialized reviews. The basic methods of flow visualization are explained and the long history of flow visualization is sketched by tracing the introduction of major methods and of discoveries made by flow visualization. Limitations and problem areas in the visual evaluation of velocity and vorticity fields are discussed, and a glimpse into the future role of flow visualization is ventured.