This article describes bird species discovered since 1900. Before the 20th century, and into its early decades, the pace of discovery (and "discovery") of new species was fast; during this period, with numerous collecting expeditions into species-rich areas not previously visited by western ornithologists, up to several hundred new species per decade were being described. Many of these were of course not new to the local people, but since then, the pace has slowed, and new species are generally only being found in remote areas, or among cryptic or secretive groups of species. Nonetheless, several tens of species were described for the first time even during the 1990s. Considerable time can pass between discovery and publication, for a number of reasons.
Individual countries particularly rich in species newly described during this period are:
A number of individuals have been particularly prolific in describing new species, such as: