Several researchers analyse organisational forms as an idealised historical evolution were new organisational forms builds on earlier established forms. These idealised theoretical approaches have the advantages of creating an overall understanding of the variety of organisations that can be observed at a given time. They also explain this variety with a simple evolutionary logic: New organisational innovations occur in established forms. If they prove competitive they will be imitated and, with time, new forms will emerge. Hereby organisational development is not only a question of situational fit, but also due to historical dependencies. Different contributions observe different forms and give different theoretical explanations. This paper suggests an extensive framework of different organisation forms and links this framework to an elaborated theoretical analysis based on new institutional economics and other fields of organisation theory. The theoretical analysis is based on the four co-coordination mechanisms authority, rules, price and ideology. The organisational development is analysed as a stepwise development where forms develop from one level to another with time and increased scale. At the first level the Simple hierarchy and the Adhocratic form is identified. At a second level the U-form and the Professional form follows. At the third level, the M-form and H-form of large enterprises are identified. Finally, at a fourth level a new form, the W-form, is identified. The development is explained by identification of situational factors and by the use of different co-ordination mechanisms. As the idealised evolution continuous, more sophisticated forms develop which modify and extend the use the co-ordination mechanisms of earlier forms.