Hearing loss increases the cognitive demands required to attend to, and understand, an auditory message. There are numerous anecdotal reports of sustained listening effort and fatigue in individuals with hearing loss. Therefore, listening effort and fatigue might be important consequences of hearing loss that are not captured by standard audiometric procedures. The aim of the first study was to quantify real-world listening effort and fatigue in adults with hearing loss. Participants included 50 experienced hearing aid users, 50 cochlear implant users, 50 adults with single-sided deafness, and a control group of 50 adults with âgoodâ hearing. The study used the generic 10-item Fatigue Assessment Scale and a locally-developed 6-item Listening Effort Scale. The results revealed that all three groups of adults with hearing loss reported significantly greater listening effort and fatigue, relative to the control group. Listening effort (or fatigue) were not correlated with hearing level in the hearing aid group and there was no significant difference in mean effort/fatigue between the three groups. The main aim of the second study was to investigate the correlation between hearing handicap and self-reported listening effort and fatigue. Participants included 86 adults with hearing loss, some of whom were hearing aid users. Handicap was measured using the 25-item Hearing Handicap Inventory for the Elderly. The results revealed a significant positive correlation between hearing handicap and both listening effort and fatigue. These findings are consistent with models and frameworks of listening effort and fatigue, which suggest that fatigue is a motivational control mechanism i.e., fatigue will be experienced if sustained effort is not perceived as rewarding. During the preparation of this thesis, there has been an explosion of peer-reviewed publications on the topic of listening effort and fatigue; however, the literature is as confusing as it is voluminous: potential measures of listening effort and fatigue (self-report, behavioural, and physiological) frequently do not correlate with each other and sometimes result in contradictory findings. This raises questions about the sensitivity and reliability of the different measures along with the possibility that listening effort is a multidimensional phenomenon. Therefore, the aim of the final study was to investigate the reliability of potential measures of listening effort, to identify if they correlate with each other, and to use Factor Analysis to identify if the different measures tap into the same underlying dimension. Listening effort was measured simultaneously using multi-modal measures including: pupillometry, EEG alpha power, skin conductance, reaction time, and self-report. Recordings were obtained while 116 participants, with normal to severe hearing loss, performed a speech-in-noise task. Results revealed that the measures are mostly reliable. There were weak or non-significant correlations between the measures. Factor Analysis revealed that the measures grouped into four underlying dimensions, which we interpret as: i) performance, ii) cognitive processing, iii) alertness, and iv) behavioural consequences. The findings of this PhD thesis revealed that high levels of listening effort and fatigue are common amongst adults with hearing loss. This suggests that a more comprehensive assessment of hearing disability should include measures of listening effort/fatigue. Further, the findings revealed that listening effort and fatigue correlate with perceived difficulties but not hearing level. The relationship between hearing level and effort/fatigue, like hearing impairment and hearing handicap, is not straightforward. Finally, measures of listening effort tap into independent dimensions. This latter finding provides a framework for understanding and interpreting listening effort, and has widespread implications for both research and clinical practice.