Among the important changes in the ICD-11 is the addition of 21 new mental disorders. New categories are typically proposed to: a) improve the usefulness of morbidity statistics; b) facilitate recognition of a clinically important but poorly classified mental disorder in order to provide appropriate management; and c) stimulate research into more effective treatments. Given the major implications for the field and for World Health Organization (WHO) member states, it is important to examine the impact of these new categories during the early phase of the ICD-11 implementation. This paper focuses on four disorders: complex post-traumatic stress disorder, prolonged grief disorder, gaming disorder, and compulsive sexual behaviour disorder. These categories were selected because they have been the focus of considerable activity and/or controversy and because their inclusion in the ICD-11 represents a different decision than was made for the DSM-5. The lead authors invited experts on each of these disorders to provide insight into why it was considered important to add it to the ICD-11, implications for care of not having that diagnostic category, important controversies about adding the disorder, and a review of the evidence generated and other developments related to the category since the WHO signaled its intention to include it in the ICD-11. Each of the four diagnostic categories appears to describe a population with clinically important and distinctive features that had previously gone unrecognized as well as specific treatment needs that would otherwise likely go unmet. The introduction of these categories in the ICD-11 has been followed by a substantial expansion of research in each area, which has generally supported their validity and utility, and by a significant increase in the availability of appropriate services.