<p>As a primary mode of human interaction, speech consists of two fundamental sound categories, i.e., vowels and consonants. This overview paper begins by providing an overview of the relative contributions of vowels and consonants to speech understanding. Their significance in speech understanding varies depending on the type of stimulus, the language, and the hearing abilities of the listener. With outcomes of these perceptual studies, a number of applications have been developed, including speech recognition, speech enhancement, auditory prosthetic devices, language acquisition, and speech privacy protection. By processing vowels and consonants, these speech technologies and applications have a significant impact on everyday life. Finally, the future research challenges in this field are outlined.</p>