Apraxia of speech (AOS), also called verbal apraxia, is a speech sound disorder affecting an individual's ability to translate conscious speech plans into motor plans, which results in limited and difficult speech ability. By the definition of apraxia, AOS affects volitional (willful or purposeful) movement pattern. However, AOS usually also affects automatic speech.

People with AOS have difficulty connecting speech messages from the brain to the mouth. AOS is a loss of prior speech ability resulting from a brain injury such as a stroke or progressive illness.

Developmental verbal dyspraxia (DVD), also known as childhood apraxia of speech (CAS) and developmental apraxia of speech (DAS), is an inability to utilize motor planning to perform movements necessary for speech during a child's language learning process. Although the causes differ between AOS and DVD, the main characteristics and treatments are similar.

Apraxia of speech (AOS) is a neurogenic communication disorder affecting the motor programming system for speech production. Individuals with AOS demonstrate difficulty in speech production, specifically with sequencing and forming sounds. The Levelt model describes the speech production process in the following three consecutive stages: conceptualization, formulation, and articulation. According to the Levelt model, apraxia of speech would fall into the articulation region. The individual does not have a language deficiency, but has difficulty in the production of language in an audible manner. Notably, this difficulty is limited to vocal speech, and does not affect sign-language production. The individual knows exactly what they want to say, but there is a disruption in the part of the brain that sends the signal to the muscle for the specific movement. Individuals with acquired AOS demonstrate hallmark characteristics of articulation and prosody (rhythm, stress or intonation) errors. Coexisting characteristics may include groping and effortful speech production with self-correction, difficulty initiating speech, abnormal stress, intonation and rhythm errors, and inconsistency with articulation.

Wertz et al., (1984) describe the following five speech characteristics that an individual with apraxia of speech may exhibit:

Apraxia of speech can be caused by impairment to parts of the brain that control muscle movement and speech. However, identifying a particular region of the brain in which AOS always occurs has been controversial. Various patients with damage to left subcortical structures, regions of the insula, and Broca's area have been diagnosed with AOS. Most commonly it is triggered by vascular lesions, but AOS can also arise due to tumors and trauma.

Stroke-associated AOS is the most common form of acquired AOS, making up about 60% of all reported acquired AOS cases. This is one of the several possible disorders that can result from a stroke, but only about 11% of stroke cases involve this disorder. Brain damage to the neural connections, and especially the neural synapses, during the stroke can lead to acquired AOS. Most cases of stroke-associated AOS are minor, but in the most severe cases, all linguistic motor function can be lost and must be relearned. Since most with this form of AOS are at least fifty years old, few fully recover to their previous level of ability to produce speech.

Other disorders and injuries of the brain that can lead to AOS include (traumatic) dementia, progressive neurological disorders, and traumatic brain injury.