Mosquitoes generate sounds by flapping their wings in flight, which are thought to have a role in acoustic communication. Furthermore, the auditory organs of mosquitoes are the most sensitive among all arthropods reported so far. However, the function of hearing in mosquitoes is still unclear, and various debates have been raised in the scientific community. This book chapter reviews current knowledge about mosquito hearing and is directed to the mosquito ecology community. First, we review acoustical aspects of hearing, which need to be taken into account to understand the capabilities of insect sensory systems across a range of distances (near-field/far-field, active/reactive field and air particle velocity/pressure). Second, the basic mechanism of antennal hearing is explained in terms of sound-level and frequency sensitivities, interactions with the Johnston's organ and spatial hearing. Third, we review a range of theories behind the role of the acoustic interactions between male and female mosquitoes (harmonic convergence, rapid frequency modulation and species-specificity), and discuss some of the main interpretations of these behaviours. Finally, we discuss the hearing range of mosquitoes in relation to communication and sound traps.