Language disorders or language impairments are disorders that cause persistent difficulty in the acquisition and use of listening and speaking skills. These difficulties may involve any of the five domains of language: phonology, syntax, morphology, semantics, or pragmatics. Language disorders may affect listening comprehension, spoken language expression, reading comprehension, and/or written expression. There are two main categories of language disorders: expressive, which involves a difficulty using words to communicate, and receptive, which involves a difficulty understanding language. Language disorders may persist across the life span, and symptoms may change over time. A language disorder can occur in isolation or in the presence of other conditions. Language disorders may occur from birth or early childhood, or they may be acquired later from disease or injury.

In the United States, speech language pathologists screen, assess, diagnose, and treat language disorders.

Though the words language and speech are often colloquially used interchangeably, they have different meanings in the context of communication disorders. Language refers to the code used for transforming mental events into words and phrases that can be perceived by other people. Language disorders, then, are specific deficits in language comprehension, the ability to understand meaning from language; and language expression, the ability to encode ideas into language forms. Language disorders are distinct from speech disorders, which involve difficulty with the act of speech production, but not with the content of the communicative message. Speech refers specifically to the ability to properly produce sounds via the oral mechanism. Speech and language disorders can occur separately or together.

The term developmental language disorder (DLD) is used to refer to a spoken language disorder that is a primary disability without a known medical cause and persisting beyond childhood. This term is also used when the language disorder co-occurs with other diagnoses, but the causal relationship is not as obvious. Some research and legislation refers to this as a specific language impairment. Adults with DLD tend to struggle with finding words or organizing their thoughts in a way that is easy for the listener to comprehend. Children with DLD may use simple or ungrammatical sentences that are more age-appropriate for a much younger child. Current data indicates that approximately 7% of young children display developmental language disorder, with boys being diagnosed twice as often as girls in young children. People with language disorders often have trouble learning to read and write. Language disorders are also often found co-occurring with other neurodevelopmental and learning disorders, such as behavioral disorders, autism, Down syndrome, dyslexia, and attention deficit hyperactivity disorder. Preliminary research on potential risk factors have suggested biological components, such as low birth weight, prematurity, general birth complications, trauma, and male gender, as well as family history and low parental education can increase the chance of developing developmental language disorder.

The term aphasia is used to refer to an acquired language disorder, usually resulting from damage to the left hemisphere of the brain, that affects language processing. Aphasia may be caused by a stroke, traumatic brain injury, or various neurodegenerative diseases. There are various types of aphasia, depending on the area of the brain affected. Below is a non-comprehensive list of some of the more common types of aphasia.

Wernicke's aphasia is characterized by impaired language comprehension for both spoken and written language, caused by damage to Wernicke's area. Patients with Wernicke's aphasia can still speak with normal fluency and prosody, and follow grammatical rules with normal sentence structure. However, they may exhibit difficulty with repetition tasks, naming items, and written word spelling.

People with Wernicke's aphasia often exhibit other forms of aphasia. Phonemic paraphasia refers to making errors in the selection of phones, a vowel or consonant sound, including errors of addition, omission, or change in position. Semantic paraphasia is a common feature of Wernicke's aphasia that involves fluent speech that contains paraphasic errors resulting from the failure to select the proper words to convey one's ideas. This deficiency can be partially compensated for using paraphrases that rely on generic terms to stand in for the hard-to-find specific words.

Transcortical sensory aphasia (TSA) has a lot in common with Wernicke's aphasia, as the causation brain damage are in areas of the brain very close to each other. Patients with TSA are able to produce connected, flowing speech that often lacks meaning due to word errors and invented words.