Dr. O'Brien is best known for her work in the area of user engagement with technology, where she has contributed numerous publications, including two recent books, Why Engagement Matters: Cross-Disciplinary Perspectives and Innovations on User Engagement with Digital Media (edited with Paul Cairns, 2016) and Measuring User Engagement (authored with Mounia Lalmas and Elad Yom-Tov, 2014), as well as the User Engagement Scale (UES), an experiential questionnaire that is used internationally to understand digitally mediated user experiences.