Recent revisions of personality disorder (PD) classifications have moved from categorical diagnoses toward dimensional models, raising renewed questions about the nosological status and clinical utility of borderline personality disorder (BPD). This narrative review traces the development of the borderline construct from early descriptions of patients positioned between neurosis and psychosis, through its theoretical consolidation within the concept of borderline personality organization, to the operationalization of BPD in DSM-III and subsequent diagnostic revisions. A central section summarizes contemporary controversies regarding the validity and utility of BPD features. Arguments for abandoning the diagnosis emphasize the absence of a distinct borderline factor in factor analytic studies, the tendency of the construct to capture fluctuating symptoms and patterns of behaviour rather than stable maladaptive personality traits, the stigmatizing and non-selective use of the label, and the lack of disorder-specific treatment approaches. In contrast, converging evidence supports the view that core borderline symptoms frequently function as markers of general PD pathology and of the severity of impairments in self and interpersonal functioning. The paper integrates the concept of the borderline level of personality functioning, conceptualizing borderline pathology as a dynamic dimension of dysfunction with potential transient regressions, and links this concept to the Level of P • Dimensional assessment of personality disorders should integrate both severity rating and trait-based description, with borderline features serving as clinically useful indicators of regression proneness and the need for specialized psychotherapeutic intervention. Abstract Recent revisions of personality disorder (PD) classifications have moved from categorical diagnoses toward dimensional models, raising renewed questions about the nosological status and clinical utility of borderline personality disorder (BPD). This narrative review traces the development of the borderline construct from early descriptions of patients positioned between neurosis and psychosis, through its theoretical consolidation within the concept of borderline personality organization, to the operationalization of BPD in DSM-III and subsequent diagnostic revisions. A central section summarizes contemporary controversies regarding the validity and utility of BPD features. The paper integrates the concept of the borderline level of personality functioning, conceptualizing borderline pathology as a dynamic dimension of dysfunction with potential transient regressions, and links this concept to the Level of Personality Functioning (LPF, Criterion A) within the DSM 5 Alternative Model for Personality Disorders (AMPD). Retaining borderline pathology as a dimension may support contemporary PD assessment by offering a clinically recognizable marker of overall dysfunction, a guide for rating severity, an indicator of personality structure and need for psychotherapy, without disrupting continuity with an extensive clinical and research tradition. Introduction: Nosological History Dimensional reforms of personality disorders (PD) classifications have challenged the status of long-standing categorical diagnoses, with BPD becoming a focal point of debate. Within official diagnostic classifications, the term borderline first appeared in the diagnosis of BPD, introduced as a distinct entity in DSM-III (1980), largely through the work of Spitzer and colleagues, building on earlier research by Gunderson and Kernberg’s concept of borderline personality organization (BPO) [ 1 ]. As a narrative review, the literature selection was guided by conceptual relevance and the authors’ expertise rather than by systematic inclusion and exclusion criteria. Priority was given to foundational theoretical works on borderline personality organization, borderline level of functioning and dimensional models, WHO Working Group for ICD-11 Personality Disorders Classification publications, major longitudinal studies of BPD course and outcome, and recent empirical contributions to the dimensional classification debate. Within this framework, the concept of pseudo-borderline syndrome was introduced to describe a clinical presentation in which individuals whose baseline personality functioning is neurotic, characterized by integrated identity, mature defense organization, and intact reality testing, transiently exhibit borderline features (affective instability, diffuse identity, impulsive behavior, transient paranoid ideation) during the course of an affective disorder, most commonly major depression or dysthymia. Crucially, these borderline symptoms remit with successful treatment of the affective episode, revealing that the borderline presentation was state-dependent rather than reflecting a structural personality deficit [ 34 , 35 ]. The concept was developed on the basis of clinical observations that dysthymic disorder significantly distorts personality assessment, producing apparent borderline features that resolve when the affective condition is treated [ 35 ]. Sharp has argued that borderline criteria capture precisely what LPF is designed to measure, that is, self and interpersonal functioning, which is why they represent general personality pathology rather than forming a distinct specific factor [ 28 ]. Conceptually, the LPF domains of self-functioning (identity and self-direction) and interpersonal functioning (empathy and intimacy) correspond to the self and object representations that psychodynamic models place at the core of personality organization. The more severe the PD, the more likely borderline symptoms are to manifest. Rather than demonstrating that the borderline pattern is dispensable, this finding is consistent with the interpretation that it functions as a clinically recognizable marker of moderate to severe PD, precisely the role proposed by the