DEMO (Design and Engineering Methodology for Organisations) comprises a Way of Thinking (WoT), a Way of Modelling (WoM) and a Way of Working (WoW). The WoT consists of a number of theories. The WoM consists of an integrated whole of four aspect or sub-models: the Cooperation Model (CM), the Action Model (AM), the Process Model (PM) and the Fact Model (FM). The CM of a Scope of Interest (SoI) is the ontological model of its construction, thus of the identified transactor roles and the coordination structures among them: the interaction structure, the interimpediment structure and the interstriction structure. The AM of an SoI is the ontological model of its operation. For every actor role in the focus (of the SoI), it provides the rules that guide the role fillers in doing their work. The guidelines for responding to coordination events are called action rules; the ones for performing production acts are called work instructions. The PM of an SoI is the ontological model of the state space and the transition space of its coordination world. It contains the existence laws and occurrence laws for all transaction kinds in the SoI. The FM of an SoI is the ontological model of the state space and the transition space of its production world. It contains the existence laws and occurrence laws for all identified entity types, value types, property types, attribute types and event types. The four sub-models are expressed in the DEMO Specification Language (DEMO-SL), which comprises diagrams, tables and formal textual descriptions. For producing essential models of enterprises, the WoW of DEMO offers the OER method (Organisational Essence Revealing). It consists of a number of steps in which the four DEMO models are produced, preferably in a spiral way. For (re)developing organisations as well as for developing Enterprise Information Systems, DEMO offers the DAO method, which is an acronym for Designing under Architecture from Ontology.