A language delay is a language disorder in which a child fails to develop language abilities at the usual age-appropriate period in their developmental timetable. It is most commonly seen in children ages two to seven years-old and can continue into adulthood. The reported prevalence of language delay ranges from 2.3 to 19 percent.

Language delays are distinct from speech delays, in which the development of the mechanical and motor aspects of speech production are delayed. Many tend to confuse language delay with speech delay or even just late talker. All of these have different telltale signs and determining factors. Speech delay seems to be more similar to late talker compared to language delay. Speech is the verbal motor production of language, while language is a means of communication. Because language and speech are independent, they may be individually delayed. For example, a child may be delayed in speech (i.e., unable to produce intelligible speech sounds), but not delayed in language because they use a Sign Language. Additionally, language delay encompasses the entirety of language developmental progress being slowed and not just the speech aspects.

Language delays are recognized by comparing language development of children to recognized developmental milestones. They are presented in a variety of ways, as every individual child has a unique set of language skills and deficiencies that are identifiable through many different screenings and tools. There are different causes leading to language delay; it is often a result of another developmental disorder and treatment requires analysis of the unique individual causes. The condition is frequently observed early on, among two- and three-year-olds. Early language delays are only considered risk-factors in leading to more severe language disorders.

The anatomical language centers of the brain are the Broca's and Wernicke's area. These two areas include all aspects of the development of language. The Broca's area is the motor portion of language at the left posterior inferior frontal gyrus and involves speech production. The Wernicke's area is the sensory portion of language at the posterior part of the left superior temporal gyrus and involves verbal comprehension.

There are recognizable speech and language developmental milestones in children. For children with language delays, milestones in their language development may be different or slowed. Recent studies have shown the different milestones for children with language delay compared to children with normal language development. Language delays are often identified when a child strays from the expected developments in the timeline of typical speech and language developmental milestones that researchers agree on. Children can stray slightly from the confines of the expected timeline; however, if a child is observed to be largely straying from the expected timeline, the child's caretaker should consult with a medical specialist.

This timeline only provides a very general and brief outline of expected developments from birth to age five, individual children can still exhibit varying development patterns as this timeline only serves as a general guideline. This timeline is only one model, other models regarding language development exist. The development of language remains a theoretical mystery.

Around 2 months, babies can make "cooing" sounds.

Around 4 months, babies can respond to voices.