Participation in recreational sport and physical activity (PA) provides many health benefits, particularly for students within higher education. For example, participation can reduce the likelihood of chronic conditions and enhance cognitive functioning. Despite these benefits, a large majority of students do not meet recommended guidelines to achieve such health benefits. However, the transitioning period of first-year students to university renders the university setting an ideal opportunity to promote health behaviours. Interventions targeting health improvements should be developed using the insights of health psychological theory, especially as such theory enables relevant psychological determinants to be identified for intervention. The current thesis aimed to develop and implement theory-based interventions targeting first-year students’ participation in recreational sport and PA. Five empirical studies are presented within the thesis. Two studies identified first-year university students’ motivations towards participation in recreational sport using the Theory of Planned Behaviour (TPB). Study 1 identified the salient behavioural, normative and control beliefs underlying students’ participation and Study 2 identified the critical beliefs influencing participation. Following this, Study 3 identified the behaviour change techniques (BCTs) relevant to changing these beliefs. Studies 4 and 5 then adopted the short message service (SMS) delivery mode to deliver interventions targeting students’ participation in recreational sport and PA through manipulating attitude and goal priority. The studies provide support for the TPB in developing and undertaking interventions promoting two important health behaviours. Interventions promoting university recreational sport should target the key beliefs identified in the thesis and should utilise the identified BCTs and additional content to do so. Research attempting to change students’ rates of PA should adopt similar text messages to change key psychological determinants. Future work is needed to examine the characteristics influencing the effectiveness of the goal priority strategy within the SMS delivery mode.