ISO 24617-2:2012 provides a set of empirically and theoretically well-motivated concepts for dialogue annotation, a formal language for expressing dialogue annotations -- the dialogue act markup language (DiAML) -- and a method for segmenting a dialogue into semantic units. This allows the manual or automatic annotation of dialogue segments with information about the communicative actions which the participants perform by their contributions to the dialogue. It supports multidimensional annotation, in which units in dialogue are viewed as having multiple communicative functions. The DiAML language has an XML-based representation format and a formal semantics which makes it possible to apply inference to DiAML representations. ISO 24617-2:2012 specifies data categories for reference sets of communicative functions and dimensions of dialogue analysis and provides principles and guidelines for extending these sets or selecting coherent subsets of them. Additionally, it provides guidelines for annotators and annotated examples. It is applicable to spoken, written and multimodal dialogues involving two or more participants.