Obsessive-compulsive personality disorder (OCPD) is a severe mental health condition estimated to affect 2-7% of the population (American Psychiatric Association [APA], 2013; Grant et al., 2004), making it one of the most common personality disorders (PDs). It is currently operationalised by reference to several behavioural symptoms, including a preoccupation with details, rules and orderliness, over-conscientiousness, perfectionism, hoarding, excessive devotion to work and productivity, reduced capacity to express warmth and emotion, and mental and interpersonal control at the expense of flexibility, openness and efficiency (APA, 2013). The disorder has a long history in the clinical literature, being included in all versions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) (APA, 1952-2013). Despite its history, prevalence and severity, OCPD has been the subject of only limited research. DSM-5 Section III (APA, 2013) includes a newly developed hybrid dimensional-categorical diagnostic model for PDs: the Alternative Model of Personality Disorders (AMPD). The AMPD operationalises PDs using disorder-specific constellations of maladaptive personality traits and functional impairment. Studies assessing the personality traits relevant to OCPD have had inconsistent results, and research into the impairment profile of OCPD is limited. Additional research is required to refine the alternative model of OCPD. This research project aimed to help meet this need. Study One examined the validity of a newly developed disorder-specific impairment scale for OCPD. Although the measure showed initial promise in its ability to measure-disorder specific impairment, results indicated that it may not be useful to maintain the distinction, made in the AMPD, between personality impairment in the self and interpersonal domains. Study Two evaluated the extent to which specific personality traits, and scores on the measure of OCPD-specific impairment from Study One, accounted for variance in scores on measures of traditional OCPD (as operationalised in DSM-5 Section II). Results showed that three of the four AMPD traits, as well as two additional traits uniquely accounted for a large proportion of variance in a latent variable of traditional OCPD. Study Three examined the extent to which the trait criteria in the alternative model of OCPD corresponded with the traditional operationalisation of OCPD with a particular focus on the individual OCPD criteria, in a Danish clinical sample. Results revealed that the AMPD traits aligned only partially with the traditional conceptualisation of OCPD, and that additional traits may be relevant to further capture the nuances of this personality disorder. Study Four investigated the extent to which self-report and informant data of personality psychopathology correspond, the optimal trait profile for OCPD in the AMPD, and whether an OCPD-specific measure of impairment is more diagnostically useful than measures of general impairment in personality functioning. Results showed that self-report data moderately corresponded with informant data and that rigid perfectionism can be considered a core trait of OCPD. OCPD-specific impairment accounted for more variance in traditional OCPD than general measures of impairment. While additional research into the utility of the AMPD is required, taken together, these studies generally support the use of the hybrid dimensional-categorical approach in the assessment and diagnosis of OCPD.