The paper presents a phylogenetic species concept (PSC) that defines species as the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphorons). This concept is based on the idea that species are the smallest units that can be analyzed using cladistic methods and are interpretable as the result of phylogenetic history. The PSC is characterized by a focus on patterns of character distribution and is consistent with current explanations of speciation processes. It is argued that the PSC is more logically primary than alternative species concepts and is compatible with various biological needs for species. The PSC is contrasted with other species concepts, such as the biological species concept, which is based on reproductive isolation and is difficult to apply to many taxonomic groups. The PSC is also contrasted with autapomorphic species concepts, which rely on unique traits to define species. The paper discusses the differences between phylogenetic and tokogenetic systems of relationship, and argues that the PSC is more appropriate for cladistic analysis. The PSC is also discussed in the context of asexual and clonal species, and it is argued that the PSC can recognize these as distinct species. The paper concludes that the PSC is a valuable concept for evolutionary biologists as it provides an independent and objective means of identifying and differentiating the products of tokogeny and the elements of phylogeny.The paper presents a phylogenetic species concept (PSC) that defines species as the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphorons). This concept is based on the idea that species are the smallest units that can be analyzed using cladistic methods and are interpretable as the result of phylogenetic history. The PSC is characterized by a focus on patterns of character distribution and is consistent with current explanations of speciation processes. It is argued that the PSC is more logically primary than alternative species concepts and is compatible with various biological needs for species. The PSC is contrasted with other species concepts, such as the biological species concept, which is based on reproductive isolation and is difficult to apply to many taxonomic groups. The PSC is also contrasted with autapomorphic species concepts, which rely on unique traits to define species. The paper discusses the differences between phylogenetic and tokogenetic systems of relationship, and argues that the PSC is more appropriate for cladistic analysis. The PSC is also discussed in the context of asexual and clonal species, and it is argued that the PSC can recognize these as distinct species. The paper concludes that the PSC is a valuable concept for evolutionary biologists as it provides an independent and objective means of identifying and differentiating the products of tokogeny and the elements of phylogeny.