The fifth edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and the eleventh edition of the World Health Organization’s International Classification of Diseases (ICD-11) chapter on mental and behavioural disorders represent interrelated milestones in the understanding of psychiatric (mental) disorders. Following a brief history of the scientific and professional forces that contributed to their rise as international standards, there is a succinct summary of their characteristics, similarities, and differences. Their advantages and limitations for research, specialty clinical, and primary care clinical use are identified, as is the need for a briefly described ICD-11 primary care version (ICD-11-PC). Likewise, the need for, and development of, a separate International Classification of Functioning, Disability, and Health (ICF) is described that is now more closely linked to these mental disorder classifications. These interim classifications now await further understanding of the aetiology and pathophysiology for iterative advances.