Listening effort refers to the mental exertion required to attend to and understand an auditory message. Listening-related fatigue refers to the extreme tiredness resulting from repeated (and/or sustained) incidences of effortful listening. Hearing-impaired adults commonly report listening-related effort and fatigue. Hearing-impaired children have also been found to exhibit dysfunctional levels of stress compared to their normal-hearing counterparts. The physiological mechanisms that underpin listening-related effort and fatigue are not yet clearly understood. The aim of the thesis was to investigate different measures of listening-related effort and fatigue in three related studies. In study one, the effect of signal-to-noise ratio (SNR) and masker intelligibility on response time - a potential objective measure of listening effort - was examined in a group of young adults. Mean response time was slower in the more adverse SNR condition and in the presence of an intelligible masker. In study two, response time and pupillometry were used to measure listening-related effort and fatigue in a group of young adults. Pupil size revealed changes in physiological arousal consistent with an increase in both listening-related effort and fatigue in a more adverse SNR. In the final study, response time and pupillometry were used to examine listening-related effort and fatigue in 8 - 11 year old children. Pupil size revealed changes in physiological arousal consistent with an increase in listening effort, but not fatigue, in a classroom-like SNR. In conclusion, this thesis contributes to our knowledge of listening-related effort and fatigue in three notable ways: (i) response times are shown to be sensitive to interference from an intelligible masker during a listening task, (ii) evidence of listening-related fatigue was found using pupillometry in a group of young adults, and (iii) evidence of listening effort was found using pupillometry in school-aged children at a classroom-like SNR. A sensitive and reliable measure of listening-related effort and/or fatigue could be of clinical value for hearing health practitioners in determining intervention success and ultimately mitigating the disability associated with hearing loss.