Discovery and naming
The elfin woods warbler is one of many species in the
Setophaga of the
New World warbler family Parulidae. It was first observed in 1968 by Cameron and
Angela Kepler while they were conducting observations on two
Puerto Rican endemic birds, the
Puerto Rican amazon and the
Puerto Rican tody. On May 18, 1971, a specimen was captured in
El Yunque National Forest, which at the time was believed to be its only habitat. A year later Kepler and Parkes described and named the species, making it the most recent warbler of the genus Setophaga discovered in the New World.
 Also, it is the first species described in the
Caribbean since 1927 and the first Puerto Rican species described in the 20th century.
 The specific name, angelae, is a tribute to Angela Kepler. Elfin-woods warbler is an alternative spelling, and Reinita de Bosque Enano is the
Spanish name. The species was initially placed in the genus Dendroica, but in 2011 the
American Ornithologists' Union reorganized the classification of the family Parulidae and transferred species in Dendroica to Setophaga.
 This revised classification was adopted by the
International Ornithologists' Union.
A phylogenetic analysis using
mitochondrial DNA sequences from New World warblers has shown that, within the genus Setophaga, the elfin woods warbler is most closely related to the
arrowhead warbler, a species which is endemic to
Jamaica, and the
plumbeous warbler, which is endemic to the islands of