Developmental language disorder (DLD) is a common neurodevelopmental condition affecting approximately 7% of the population. Although it is usually diagnosed in early childhood, it is a lifelong condition, impacting the development and use of spoken language throughout life. This in turn can have a widespread impact on literacy and educational achievement, employment outcomes, as well as socioemotional well-being and mental health. Both genetic and environmental factors are thought to play a role in DLD, but the specific factors involved have not yet been specified. Neurobiologically, DLD is associated with atypical structure and function of cortical and subcortical brain regions that support language learning. At the cognitive level, current theories propose that difficulties in detecting and retaining auditory sequences in the language input may be an important proximal cause of the language difficulties that characterize DLD. A range of other perceptual and cognitive processes may also be causally involved, including speech perception, speed of information processing, and working memory. In addition, some individuals with DLD may have co-occurring difficulties in areas outside language, such as early sleep, motor skills, attention and executive functions, and emotion processing. As with other neurodevelopmental conditions, it is now recognized that the etiology of DLD is likely to be complex, and that a constellation of risk and protective factors combine to produce the particular profile of strengths and weaknesses in any given person: thus, individuals with DLD may vary considerably in terms of their language profile, and there is frequent overlap with conditions such as dyslexia, attention-deficit/hyperactivity disorder, or autism. It follows that, in addition to optimizing speech-language interventions that target the primary language difficulties, it is important to take a whole-person approach in supporting people with DLD to thrive.