This foundational review outlines the conceptual, historical, and methodological roots of modern behavioral threat assessment. Synthesizing developments from forensic psychology, law enforcement, psychiatry, intelligence analysis, and organizational risk management, the authors trace how the field shifted from trait-based profiling toward dynamic, behavioral, and situational models of targeted violence. Key constructs—including grievance, ideation, planning, preparation, fixation, identification, and last-resort thinking—are contextualized within emerging empirical findings. The article examines the operational value of warning behaviors, attack-time pathways, and multidisciplinary team structures, emphasizing the importance of iterative information-gathering and hypothesis testing. Practical challenges such as uncertainty, false positives, organizational blind spots, and communication breakdowns are explored. The paper concludes by proposing core principles that define threat assessment as a preventive, evidence-informed, and decision-focused practice.