The Clinical descriptions and diagnostic requirements for ICD-11 mental, behavioural and neurodevelopmental disorders (CDDR) is a comprehensive diagnostic manual designed to support the accurate and reliable identification and diagnosis of these disorders in clinical settings across the world. Based on reviews of the latest available scientific evidence and best clinical practices, the CDDR were developed and tested through a rigorous, multi-disciplinary and participatory approach involving hundreds of experts and thousands of clinicians around the world. An accurate diagnosis is generally the first step towards appropriate care and treatment. By supporting accurate and timely diagnosis of mental, behavioural and neurodevelopmental disorders, the CDDR will ultimately ensure more people are able to access services that meet their needs. The ICD-11 CDDR are aimed at: - mental health professionals and non-specialist health professionals such as primary care physicians responsible for assigning these diagnoses in clinical settings; - other health professionals in clinical and non-clinical roles, such as nurses, occupational therapists and social workers, who need to understand the nature and symptoms of mental, behavioural and neurodevelopmental disorders even if they do not personally assign diagnoses; and - students and trainees in mental health and other health fields who need to gain an understanding of the nature and symptoms of mental, behavioural and neurodevelopmental disorders as part of their education and training. WHO’s Eleventh Revision of the International Classification of Diseases (ICD-11) is the global standard for recording and reporting diseases and health related conditions. It provides standardized nomenclature and a common health language for WHO member states, health systems and health practitioners across the world. ICD-11 was adopted by the 72nd World Health Assembly in May 2019 and came into effect as a basis for health reporting in January 2022. The CDDR are a clinical version of ICD-11 and thus complementary to the system for the statistical reporting of health information, referred to as the linearization for mortality and morbidity statistics (MMS).