ISO 18104:2014 specifies the characteristics of two categorial structures, with the overall aim of supporting interoperability in the exchange of meaningful information between information systems in respect of nursing diagnoses and nursing actions. Categorial structures for nursing diagnoses and nursing actions support interoperability by providing common frameworks with which to analyse the features of different terminologies, including those of other healthcare disciplines, and to establish the nature of the relationship between them, develop terminologies for representing nursing diagnoses and nursing actions, develop terminologies that are able to be related to each other, and establish relationships between terminology models, information models and ontologies in the nursing domain.It is applicable to the following user groups: developers of terminologies that include nursing diagnosis and nursing action concepts; developers of categorial structures and terminologies for other healthcare domains, to support clarification of any relationship to or overlap with nursing concepts; developers of models for health information management systems such as electronic health records and decision support systems, to describe the expected content of terminological value domains for particular attributes and data elements in the information models; developers of information systems that require an explicit system of concepts for internal organization, data warehouse management or middleware services; developers of software for natural language processing, to facilitate harmonization of their output with coding systems.It is not intended for use by clinical nurses without health informatics expertise. However, it provides an introduction to categorial structures to assist those without health informatics expertise to contribute to its development, review, implementation and evaluation.Topics considered outside the scope of ISO 18104:2014 include complete categorial structures that would cover all the potential details that could appear in expressions of nursing diagnoses and nursing actions, a detailed terminology of nursing diagnoses or nursing actions, a "state model" for diagnoses or actions ? for example, provisional diagnosis or absent diagnosis, planned action or action not to be done ? diagnoses made and actions undertaken by nurses working in other professional roles, and knowledge relationships such as causal relationships between concepts.