Two studies were performed that explore the effects of internet self-presentations on identity shift, in which a person's self-concept is changed based on self-presentation (e.g., conceptualizing oneself as more extroverted). Study 1 demonstrates that identity shift is enhanced after self-presentation online relative to an offline self-presentation. Study 2 explores the mechanism behind this effect by manipulating perceptions of audience and time available for constructing a text-based, online self-presentation. The results of Study 2 revealed that perceptions of audience size and participants' expectations of acquaintanceship with the audience predict identity shift. In both studies, certainty in the task and ease of the also task increased identity shift. These results support previous work on biased scanning as a mechanism of identity shift and expand the boundary conditions of the public commitment model. Implications for real world internet users and future system designs are discussed.