A major reconceptualization of personality psychopathology has been proposed for DSM-5 that identifies core impairments in personality functioning, pathological personality traits, and prominent pathological personality types. A comprehensive personality assessment consists of four components: levels of personality functioning, personality disorder types, pathological personality trait domains and facets, and general criteria for personality disorder. This four-part assessment focuses attention on identifying personality psychopathology with increasing degrees of specificity, based on a clinician's available time, information, and expertise. In Part I of this two-part article, we describe the components of the new model and present brief theoretical and empirical rationales for each. In Part II, we will illustrate the clinical application of the model with vignettes of patients with varying degrees of personality psychopathology, to show how assessments might be conducted and diagnoses reached. © 2011 American Psychological Association.