This chapter reviews what we know about the dispositional construct of threat sensitivity in humans. We begin by considering how this trait construct can be characterized neurobehaviorally, in terms of variations in the threshold for shifting from a goal-directed action set to an inhibitory-defensive posture when confronted with threat cues. Next, we discuss how self-report measures of constructs such as fearfulness and anxiety-proneness relate to clinical outcomes and neurobiological variables, highlighting that relations with the latter are inherently constrained by construct dissimilarity and method mismatch. We then propose a psychoneurometric approach to quantifying dispositional threat sensitivity, entailing integration of measures from domains of self-report and neurophysiology, that can serve to bridge the gap between the trait/symptom domain and that of neurobiology, and we describe an illustration of this approach by Yancey et al. (Psychophysiology 53:393–405, 2016). Following this, we review findings from twin-biometric and longitudinal studies that provide evidence for dispositional threat sensitivity as a liability factor for internalizing disorders – in particular, conditions involving excessive circumscribed fear (i.e., phobias, panic disorder). We conclude with a brief recap and some suggestions for future research.