A semiotic analysis is made of the six major plays by Eugene O''Neill and an attempt is made to yield a systematic analysis towards humanistic interpretations of texts. Theoretical interpretations are enriched with discussions of the plays. Technical matters such as the segmentation of the text are specified in appendices. Six semiotic dimensions have been studied: motifs, theatrical semiotic systems, their use in communicational functions, role function of the dramatis personae, their levels of awareness, and aristotelian divisions.