Sadanobu's research on fluency and disfluency in Japanese reveals that disfluency among healthy native speakers follows predictable patterns and may actually enhance their everyday communication. The book challenges the conventional view that disfluency should simply be eliminated by demonstrating that it serves dual purposes, both as an obstacle to overcome and a valuable communicative tool that speakers learn and strategically employ in conversation. Drawing from diverse fields including linguistics, conversation analysis, language education, and language disorders research, the contributors build a compelling case for this nuanced perspective. They extend their analysis to practical applications in second language teaching and speech synthesis, presenting disfluency as a spectrum that encompasses native speakers, language learners, and language-impaired individuals. Their findings reveal that disability-induced disfluency exists on a continuum with typical speaker disfluency rather than representing a separate phenomenon. This is an essential book for academics and researchers on oral communication, especially in Linguistics and Japanese studies. The Open Access version of this book, available at http://www.taylorfrancis.com, has been made available under a Creative Commons Attribution-Non Commercial-No Derivatives (CC BY-NC-ND) 4.0 license.