Attention deficit hyperactivity disorder (ADHD) may significantly affect one's learning. Research is abundant in many scientific areas but, still, little is known about how ADHD affects second and additional language learning from linguistic and multilingualism perspectives. This entry begins with a description of common ADHD manifestations to explain the two main presentations of the condition. The second section discusses the research to date on ADHD in the context of bilingualism and multilingualism, while the final part focuses on pedagogical implications and practical recommendations. This part also poses vital questions that should be addressed by future investigations to enhance inclusive teaching approaches.