This book is written in response to several demands. Of course, the information presented in it is available in several other books and journal articles on fluency and stuttering. Nevertheless, the book puts together information that most books and journal articles have not considered in the literature commonly available in India, with the exception of articles in international journals. This information will be helpful to graduate students, researchers, and faculty, I hope. Several books have provided extensive literature on particular topics, but a comprehensive compilation is not available. Therefore, this book is written. Stuttering is a heterogenous disorder of speech, and unlike other speech disorders, it has much variability in terms of time, situation, a person with whom the Persons With Stuttering (PWS) are communicating etc. Also, it appears that there may be sub-groups among PWS. Several hypotheses have been postulated to understand normal speech production, but this area is still naïve as none of the theories address all of the questions related to stuttering and its treatment. To understand and diagnose stuttering, it is extremely important to know about fluency. Thus, this book covers definitions of fluency, disfluency and dysfluency in chapter 1, fluency development in normal children in chapter 2, the anatomical and physiological bases of fluency in chapter 3, the acoustic basis of fluency in chapter 4, genetic basis in chapter 5, and linguistic basis in chapter 6. Of course there are additional bases of fluency, such as psychological or prosodic, which are not covered in the book. The reason is that Children With Stuttering (CWS), especially in the initial stages, may not have any psychological basis, and prosody- intonation, stress, and rhythm - is difficult to measure. Yet, some parts of prosody like stress and rhythm are covered as fluency enhancers in chapters 1 and 2. Relevant journal articles are reviewed and presented where necessary. I thought that in the last chapter, I would try synthesizing all the information presented in the first six chapters. However, the views of authors are so diverse that there are probabilities of sub-groups within PWS. The data so far collected on typical children is mostly in English and it is insufficient to build a database in English or other languages. The data in English may not be useful to other languages owing to variations in phonetic and syllabic structure, stress and rhythm. Hence, a multicentric and multilingual database in typical children and adults is warranted. Though the book is titled Fluency, most of the literature comes from experiments on stuttering, or what could have contributed to fluency failures in PWS. From abnormal fluency, we are trying to deduce an understanding of normal fluency in CWS and PWS. Further, as I have observed, spectrograms and glottograms of fluency failures (repetitions) of PWS, reveal that the repetitions may be because PWS are not reaching the target phoneme and hence they keep iterating speech over and again to reach the target phoneme, which they may or may not achieve. These are mostly on respiratory, laryngeal, and articulatory efforts, neural commands, and may be the lack of coordination of these sub-systems. Most of these so called repetitions are on stop consonants and hence, the listener may be unable to differentiate the bursts, aspirations, and voicing of various stop consonants as they are very minute events. For example, a burst may be of a duration of 3-11 ms. Therefore, more carful observations on these aspects are warranted. The book is an attempt to put together what we really know about fluency and its clinical application. The final goal in the research of fluency is a complete understanding of the speech production system in typical children and adults, which is unavailable at present. But something valuable is better than nothing, and several scientists have provided it.