Twenty-five years ago, this journal published two articles reporting the development and initial validation of the 20-Item Toronto Alexithymia Scale (TAS-20). Since then the literature on alexithymia has burgeoned with the vast majority of this research using the TAS-20, including multiple language translations of the scale. In this article we review the psychometric literature evaluating various aspects of the reliability and validity of the TAS-20 and examine some of the controversies surrounding the scale and the construct it assesses. We reflect on the ways in which the TAS-20 has advanced the measurement of the construct and theory of alexithymia. We also discuss recent developments and some future directions for the measurement of alexithymia. Although not without some controversy, the preponderance of the accumulated evidence over a 25-year period supports various aspects of the reliability and validity of the TAS-20, including findings from confirmatory factor analytic and convergent and discriminant validity studies which are consistent with Nemiah et al.'s (Nemiah et al., 1976 3) and Taylor and colleagues (Taylor et al., 1997 9) theoretical formulations and definition of the alexithymia construct. Based on the accumulated empirical evidence of 25 years, we conclude that the TAS-20 is a reliable and valid instrument and accurately reflects and measures the construct as it was originally defined by Nemiah et al. Nemiah et al. (1976) 3 as composed of deficits in affect awareness and expression and pensée opératoire (operational thinking). Clinicians and researchers can use the TAS-20 to confidently measure alexithymia, the roots of which have foundations in psychosomatic medicine. •In this article we review comprehensively the 20-item Toronto Alexithymia Scale (TAS-20).•We examine some controversies surrounding the scale and the construct it assesses.•The preponderance of the accumulated evidence supports the psychometri properties of the scale.•The TAS-20 accurately reflects and measures the alexithymia construct as it was originally described by Nemiah and Sifneos.