Stuttering (known as stammering in parts of the UK and scientifically known as dysphemia) is a speech disorder in which the normal flow of speech is frequently disrupted by repetitions (sounds, syllables, words or phrases), pauses and prolongations that differ both in frequency and severity from those of normally fluent individuals. The term stuttering is most commonly associated with involuntary sound repetition, but it also encompasses the abnormal hesitation or pausing before speech, referred to by stutterers as blocks, and the prolongation of certain sounds, usually vowels. Much of what constitutes "stuttering" cannot be observed by the listener; this includes such things as sound and word fears, situational fears, anxiety, tension, shame, and a feeling of "loss of control" during speech. The emotional state of the individual who stutters in response to the stuttering often constitutes the most difficult aspect of the disorder.

About 1% of adults and 5% of children in the world are afflicted with some form of the disorder, with slightly higher percentages of affected African (8%9%) and West Indies (3%4%) adults ². Men account for approximately 80% of all stutterers, while women are much more likely to either outgrow or recover from the disorder ¹.

Stuttering is essentially neurogenic (neuropathological rather than mental) in origin, and is generally not a problem with the physical production of speech sounds (see Voice disorders) or putting thoughts into words (see Dyslexia, Cluttering). Stuttering does not affect intelligence, and apart from their speech problem, people who stutter are normal. Anxiety, low confidence, nervousness, and stress therefore do not cause stuttering, although they often worsen it. The disorder is also variable. This means that in certain situations, such as talking on the telephone, the stuttering might be increased, or it might be lessened, depending on the anxiety level connected with that activity. In other situations, such as singing (as with country music star Mel Tillis) or speaking alone (or reading from a script, as with actor James Earl Jones), fluency improves. Some mild stutterers, such as Bob Newhart, have used it to their advantage. Although the exact etiology of stuttering is unknown, both genetics and neurophysiology are thought to contribute. One theory is that an inherited genetic factor may cause the speech pathways in the brain to be less efficient, contributing to the development of a stutter. Although there are many treatments and speech therapy techniques available to help increase fluency, there is essentially no "cure" for stuttering.