Mental health treatment plans often require clients to engage in therapeutic activities in between sessions to be effective. However, despite the demonstrated efficacy of “therapy homework,” clients overwhelmingly do not engage in these activities outside of therapy. Thus therapists require nuanced, in depth information about their clients’ lived experience to tailor these therapeutic activities to clients’ life circumstances, to anticipate and address barriers that may come in the way. In this thesis, we explore therapist information needs to tailor therapeutic activities to clients’ life context, and how technology can incorporate this information to better support client engagement in therapeutic activities within and between sessions. First we investigate therapist-client collaboration challenges in setting between-session goals such as therapy homework, then further our understanding of therapist information needs through studying challenges and strategies associated with the practice of behavioral chain analysis in DBT. We contribute an empirical understanding of therapist information needs and data gathering practices to support clients in engaging in therapy activities, such as therapy homework and chain analysis. With this understanding, we propose ways in which technology can be designed to support therapists and clients in working through challenges involving memory, discomfort, and limited self-awareness to improve client engagement in therapeutic activities between sessions.