The concept of personality disorder was introduced in the twentieth century. Among the key events in the development of the personality disorder concept are the introduction and subsequent rejection of degeneration theory, the work of Kurt Schneider, the DSM-III, and dimensional models of personality disorders in DSM-5 and ICD-11. The ideas that belong to the domain of personality disorder are residues of its conceptual history. This patchwork of ideas is herein used to guide an exploration of ongoing philosophical problems. The prior concepts out of which personality disorder emerged include constitution, temperament, self, character, and personality. The concepts of constitution and temperament raise the issue of the biological basis of personality and personality disorder. Recent work in behavioral genetics supports the hypothesis that personality has a genetic component, but not that it is genetically determined. Surprisingly, the genetic component in personality may become more important in open societies where people can self-select into environments. For the concept of self, the notions of causal explanation and self-continuity are important. Recent work on the psychometrics of latent variable modeling has given new life to traditional empiricist suspicions about reifying personality traits as causal entities. Longitudinal studies indicate that there is both continuity and variability in personality and personality disorder across the life span. Character is a concept drawn from moral theory and draws attention to the close association between some personality disorders and morally disvalued states. In clinical settings, separating responsibility and blame is an important skill for working with patients diagnosed with a personality disorder. The concept of personality was once referred to self-presentation but was gradually interiorized to leading the problem of distinguishing surface versus deep features of personality. The chapter concludes with a survey of six different models regarding the nature of “disorder” in personality disorder.