It is well established that hearing aids provide benefit to people with hearing loss, yet 5% to 24% of hearing aid users do not use their hearing aids at all and 40% use them only occasionally. Non- and under-use of hearing aids imply waste of hearing health care resources and unmet communication need for people with hearing loss. Various interventions have been attempted to promote hearing aid use, but none has been effective. Hearing aid fitting appointments provide an opportunity to deliver interventions to promote hearing aid use. The I-PLAN intervention was developed based on a health-psychology behaviour change framework, the behaviour change wheel, to fill the need for interventions to promote hearing aid use. This thesis examined the effectiveness of the I-PLAN to promote hearing aid use and benefit. The first study was a systematic review aimed to identify the behaviours of hearing healthcare professionals and to examine which behaviours promote hearing aid use and benefit during hearing aid discussions. The findings revealed that audiologists typically focus on provision of information related to technical aspects of hearing aid(s) during clinical interactions. There was evidence from two pilot intervention studies that 'motivational interviewing' provided by audiologists may promote hearing aid use. The second study was a quasi-randomised controlled trial. The aim was to examine the effectiveness of the complete I-PLAN intervention delivered face-to-face by audiologists during hearing aid fitting consultations with participants allocated to either; (i) I-PLAN intervention in addition to standard care (n = 80) or (ii) standard care only (n = 80). The third study was a 2 x 2 factorial randomised controlled trial to examine the prompt and plan components of the I-PLAN, delivered in sealed envelopes at the end of the fitting consultation without direct involvement of the audiologists. Participants were randomly allocated into four groups: (i) Info only (n = 60); (ii) Info + Prompt (n = 60); (iii) Info + Plan (n = 60); and (iv) Info + Prompt + Plan (n = 60). In both studies, the primary outcome was self-reported proportion of time hearing aids were used in difficult listening situations. Secondary outcomes were hearing aid use derived from hearing aid data logging, self-reported hearing aid benefit, self-reported self-regulation and habit formation. The self-regulation and habit formation were used to measure the potential mechanisms of action of the I-PLAN intervention and its components. Outcomes were measured at six weeks post-fitting. The findings of the second study showed that the complete I-PLAN intervention, delivered by audiologists, did not promote greater hearing aid use, benefit, self-regulation or habit formation. In the third study examining the individual components of the I-PLAN, the prompt component reduced hearing aid use and self-regulation. The plan component promoted greater hearing aid use and habit formation. The combination of prompt and plan components reduced data-logged hearing aid use. The adverse effect of the prompt on hearing aid use might be mediated by reduced self-regulation. The positive effect of the plan might be mediated by formation of hearing aid use habit. In conclusion, this thesis demonstrated the effects of the I-PLAN and its components on hearing aid use via controlled trial studies for the first-time in a clinical setting. The thesis provides robust evidence for the impact of a health psychology-based intervention to promote hearing aid use that is of use to clinicians and researchers. The plan component of the I-PLAN could be delivered during hearing aid fitting appointments to promote hearing aid use and habit formation. Perhaps this is the time for research in audiology to shift attention from technology-based solutions to behaviour change strategies in order to promote greater hearing aid use and benefit.