(March 25, 2015, The Auk: Ornithological Advances)—What is a “subspecies” and why should anyone be concerned about it? Recent studies have created a lively debate around the status of the California Gnatcatcher (Polioptila californica) and other subspecies of conservation concern, and now Michael Patten of the University of Oklahoma has weighed in with a philosophical commentary in The Auk: Ornithological Advances on how we define what a subspecies is in the first place. While species are defined using reproductive and behavioral criteria, subspecies are based on the concept of morphological distinctness, that is, whether populations differ in size, shape, etc. Unlike different species, different subspecies can interbreed with each other. Patten proposes that “subspecies” should be understood to refer to “heritable geographic variation in phenotype.” This means that, to be considered subspecies, populations must be located in different geographic areas and have genetic adaptations to those areas that manifest themselves in the organisms’ appearance. Genetic analysis to determine whether subspecies is valid cannot focus on arbitrarily chosen genes, but should utilize genes connected to phenotypic differences (that is, differences in appearance). Agreeing on a common definition of what a subspecies is will provide a way forward for researchers who study subspecies and, hopefully, a better way of resolving future disputes. Read the full open-access paper at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-1.1.