Approximately thirty years ago the term alexithymia was coined but it is still open which characteristics have to be considered core symptoms of alexithymia. A selective review of recent expert definitions reveals dynamism in defining the alexithymia construct. At present, the self-report Toronto-Alexithymia-Scales (TAS) are the most frequently used measures of alexithymia. Empirical findings regarding various aspects of validity (factorial, concurrent, and experimental construct validity data) question the validity of the Toronto-Alexithymia-Scales. Alexithymia as measured by the TAS appears not to be consistently related to physiological, affect decoding or affective vigilance characteristics. The heterogeneity of the results could be due to the fact that non-alexithymic persons such as depressed or socially anxious individuals yield high scores on the TAS; on the other hand self-report appears to be in principle a methodologically inadequate approach for the assessment of alexithymia. Objective or direct measures of alexithymic characteristics as the Levels of Emotional Awareness Scale or the prototypicity analysis of mood diaries based on adjective checklists seem to be promising assessment methods for future research.