This article examines the relation between adult shyness and sensory-processing sensitivity and posits a new model in which the interaction of sensitivity and adverse childhood environment leads to negative affectivity (with the highly sensitive being more impacted), which in turn leads to shyness. Consistent with this model, two questionnaire studies (Ns = 96 and 213) supported three hypotheses: (a) sensory-processing sensitivity interacts with recalled quality of childhood parental environment to predict shyness, (b) sensory-processing sensitivity interacts in the same way with childhood environment to predict negative affectivity, and (c) the interaction effect on negative affectivity mediates the effect on shyness. Hypothesis 2 was tested and supported in an additional questionnaire study (N = 393) and also in an experiment (N = 160) that manipulated negative contemporaneous experience as an analog for adverse childhood environment.