Three studies were conducted to construct a scale to measure shyness as a trait and to examine the reliability and validity of the scale. In Study I, 803 university students completed an original version of the Trait Shyness Scale (TSS) along with some other scales assessing tendencies theoretically linked to shyness. Through item analyses, 16 items were selected for the final TSS. Scores on the TSS showed a high internal consistency (α=.890) and a high test-retest reliability (γ=.724). Thus the reliability of TSS was established. The validity of TSS was confirmed by the following results. (1) The TSS score was significantly and positively correlated with the measures of evaluation apprehension, inferiority feeling, and interpersonal anxiety. Inverse relationships were observed between the TSS score and the measures of social expressivity and emotional control. (2) Correlation between the self-rated TSS score and the others (classmates)-rated shyness score of professional schools students (N=68) was γ=.584, p<.001 (Study II). (3) In Study III, 33 university students who had previously completed TSS were videotaped while they were role-playing with other students. Two raters viewed each tape and independently rated the target person on seven impressionistic rating items, including shyness. The rating of shyness was positively correlated with TSS score (γ.=557, p<.001).