This article describes a series of studies involving 2,730 participants on the development and validity testing of the Severity Indices of Personality Problems (SIPP), a self-report questionnaire covering important core components of (mal)adaptive personality functioning. Results show that the 16 facets constituted homogeneous item clusters (i.e., unidimensional and internally consistent parcels) that fit well into 5 clinically interpretable, higher order domains: self-control, identity integration, relational capacities, social concordance, and responsibility. These domains appeared to have good concurrent validity across various populations, good convergent validity in terms of associations with interview ratings of the severity of personality pathology, and good discriminant validity in terms of associations with trait-based personality disorder dimensions. Furthermore, results suggest that the domain scores are stable over a time interval of 14-21 days in a student sample but are sensitive to change over a 2-year follow-up interval in a treated patient population. Taken together, the final instrument, the SIPP-118, provides a set of 5 reliable, valid, and efficient indices of the core components of (mal)adaptive personality functioning.