This article is devoted to pure apraxia of speech (AOS). It focuses on the characteristics of the speech disorder and the types of accompanying articulation errors. The paper presents the types of AOS, including the most recent reports on the mechanisms underlying the disorder. The author describes the relationship between AOS and oral apraxia, as well as elements of differential diagnosis between AOS, dysarthria and aphasia. The disorder is rarely or erroneously diagnosed in clinical practice due to its unrecognised mechanism and uniqueness caused by its selective nature, among other reasons. AOS and aphasia are usually concurrent disorders.