The protean/boundaryless career concepts refer to people becoming more self-directed and flexible in managing their careers in response to societal shifts in work arrangements. A sizable literature has emerged on protean/boundaryless career orientations/preferences (PBCO). Questions remain, however, about the structure of PBCO and whether they predict important criteria. The PBCO literature is largely disconnected from broader individual-level career research, making it unclear how PBCO intersect with career models based on other characteristics. We address these questions by systematically reviewing/meta-analyzing PBCO research. On the basis of 135 demographically/occupationally diverse samples from 35 countries (45,288 individuals), we find no support for traditional distinctions between protean and boundaryless orientations—protean self-directed, protean values-driven, and boundaryless psychological mobility all load onto a single general factor, labeled proactive career orientation, and are only weakly related to boundaryless physical mobility preferences. We also find that PBCO predict career self-management behaviors and career satisfaction but are less related to non-career-focused attitudes, objective success, or physical mobility behavior. PBCO are strongly related to proactivity-related and self-efficacy personality traits. We use these findings to propose an integrative model for how PBCO and other dispositions mutually influence career behavior. We discuss when PBCO may have advantages over broad traits for understanding careers, implications for counseling practice, and directions for future research.