Feature structures are an essential part of many linguistic formalisms as well as an underlying mechanism for representing the information consumed or produced by and for language engineering applications. This part of ISO 24610 provides a format for the representation, storage and exchange of feature structures in natural language applications concerned with the annotation, production or analysis of linguistic data. It also defines a computer format for the description of constraints that bear on a set of features, featurevalues, feature specifications and operations on feature structures, thus offering a means of checking the conformance of each feature structure with regards to a reference specification.