People often face the challenge of understanding speech when competing speech is present—which involves a variety of cognitive processes, such as attention and prior knowledge. We have consistently found that familiarity with a person’s voice improves the ability to understand speech-in-speech, using both naturally familiar (e.g., friends and partners) and lab-trained voices. In this talk, I will describe experiments in which we aimed to gain insights into the processes underlying the familiar-voice intelligibility benefit, and how people learn about new voices. These findings have implications for theories of speech perception, and potential applications for populations who typically find speech perception particularly challenging (e.g., older adults and individuals with hearing loss).