Technology-mediated sexual interaction (TMSI) is a behavioural domain that captures the variety of ways that people engage in interpersonal exchanges of self-created, sexual material via communication technology. People report TMSI with romantic partners more than in other relationship contexts, yet there are few theoretically driven studies on people's motives for TMSI within romantic relationships. This lack of theoretical framing in the existing TMSI research makes it difficult to organize findings across studies in a coherent way, to explain particular phenomena, and to make connections between people's technology-mediated and in-person sexual experiences. The overarching goal of this dissertation was to improve knowledge about people's motives for engaging in TMSI with a committed romantic partner. To address this goal, I produced four articles which together allowed me to: (1) develop an evidence-based grounding for TMSI; (2) address limitations in current approaches to TMSI research; and (3) apply the approach-avoidance motivational framework to examine people's motives for and outcomes of engaging in TMSI with a committed romantic partner. In Article 1, I completed a systematic literature review on definitions, prevalence, and relationship context of sexting and cybersex (two of the most common TMSI activities). I found that researcher's conceptual definitions of sexting and cybersex are virtually indistinguishable and that the prevalence of sexting and cybersex was similar when researchers used comparable definitions. From these results, I conceptualized the TMSI behavioural domain. In Article 2, I described four common conceptual and measurement problems that arise when researchers focus on activities (i.e., sexting) rather than behaviours (i.e., TMSI). These problems include: (1) imprudent focus on the medium, (2) inconsistent conceptual definitions, (3) poor measurement practices, and (4) a lack of theoretical frameworks. I argue that the solutions to these problems require construct valid measures, theory-driven research, and a shift in focus away from sexting research and towards the TMSI behavioural domain. In Article 3, I used multi-grounded theory to guide qualitative analyses of 25 interviews focused on TMSI experiences and motives in current romantic partnerships. I found that participants described their TMSI motives in terms that aligned with the approach-avoidance motivational framework. In Article 4, I conducted two separate surveys to (1) develop a construct valid measure of people's approach and avoidance motives for TMSI with a current romantic partner (Article 4.1; N = 269) and (2) examine the extent to which people's approach and avoidance motives for TMSI with a romantic partner predicted well-being outcomes (Article 4.2; N = 459). I found that people's approach and avoidance motives predicted sexual, relationship, and life satisfaction through changes in dyadic sexual desire. Overall, this dissertation contributes to and extends knowledge about people's approach and avoidance TMSI motives by focusing on theoretically driven and construct valid research practices.