Our everyday listening environment is a complex acoustic mixture that needs to be processed and filtered in order to access relevant auditory information. Cognitive resources are then required for the selective processing of a particular sound stream, and simultaneous filtering of irrelevant information. The engagement of these cognitive resources to understand an auditory message, leads to listening effort, especially in noisy environments. Listening effort has been investigated in the last two decades, using a large panel of methods. The work of this thesis aims at bringing new insights on the investigation of listening effort, first with the use of pupillometry, then based on the complementarity of different measures (subjective, behavioral and objective). A methodological investigation was first conducted on pupillometry data recorded during a word-in-noise task, among older hearing-impaired patients, with and without hearing-aids. Several analysis methods were compared, including different normalization techniques, baseline periods, and baseline durations. While the different normalization methods and baseline durations showed similar results, the choice of the baseline period turned out to have a crucial influence on conclusions. Indeed, anticipatory, pre-stimulus cognitive processes, such as attention mobilization were observed on pupil dilation when the baseline period was the most anterior, relative to the stimulus onset. The differences in pupil dilation were observed even at perfect intelligibility, highlighting the relevance of pupillometry as an objective measure of listening effort. The second axis of this work focused on the results of empirical studies in which several measures, including pupillometry, were concurrently used to assess listening effort. Empirical studies were conducted (1) in older hearing-impaired patients using subjective measures of effort and pupillometry during a word-in-noise task, (2) in normal-hearing young adults using pupillometry and sclap electroencephalography during a discrimination in noise task. The lack of correlation between self-assessed difficulty of the task and pupil responses in hearing-impaired listeners, suggests that the two measures address different aspects of effortful listening. Pupil responses allowed for the observation of anticipation processes, even at perfect intelligibility, while subjective measures described the overall perceived effort during the task. In normal-hearing young adults, the modulations of the cortical responses observed thanks to electroencephalography, were linked to the processing of the stimulation and the inhibition of the irrelevant sound source during discrimination. Pupillary responses, recorded simultaneously, brought information on participants' arousal state during the task. Results of both studies then suggest that the different measures complement each other, and that their combination can help for the understanding of the different cognitive processes involved during effortful listening. Overall, this PhD work brings insights on the use and processing of the pupillometric signal to explore listening effort. It also underlines the relevance of the use of pupillometry and its contribution for the study of listening effort, among distinct populations. Finally, it shows the complementarity of subjective and objective measures during the assessment of listening effort, supporting the idea that it is a multidimensional construct.