Ownership is a fundamental human concern. It has been explored by various disciplines and within a variety of contexts. However, previous ownership researches focus primarily on physical objects such as toys, houses and stamps, while almost no research has been conducted about the psychological ownership toward digital entities. This dissertation studies the psychological aspects of digital ownership. A conceptual model of ownership and ownership indicators is summarized first. Next, ownership marking, a behavioral manifestation that is closely tied with psychological ownership, is introduced and discussed, followed by the presentation of two experimental studies that investigated the effects of digital ownership and ownership markers on owners/users.

Study 1 examined how the similarities and differences between two of the most widely-used ownership markers—communicative and defensive markers—affect users' perception and performance. A 2 (communicative marker: present vs. absent) by 2 (defensive marker: present vs. absent) by 2 (gender of dyad: male vs. female), between-participants design (N = 88) was used for this study. Results show that ownership markers had a strong impact on users' behaviors and attitudes, and communicative markers influenced users' attitudes more than defensive markers did.

Study 2 (N = 64) further investigated contextual factors that influenced the emergence and development of ownership. A 2 (social context: cooperation vs. competition) by 2 (ownership marker: present vs. absent) by 2 (gender of dyad: male vs. female), between-participants design was used. This second study identified the effects of similarity on users' behavior and attitudes between the competitive context and ownership markers. Markers had a strong negative impact on group collaboration.

The dissertation ends with the discussion of implications for the design of computer-supported group work. Directions for future research are also suggested.