This article deals with the architecure of flexibility. It attempts to define certain basic principles for the development of the attribute of flexibility in architectural systems and to demonstrate the role of the hierarchical organization of sub-systems as a general means of providing flexibility and adaptability. One of these basic principles is the physical separation of building functions into a series of hierarchically ordered sub-systems. In addition to enhancing flexibility, the principle of separation has the additional attribute of providing a means for architects to address social questions within the framework of a total architectural theory. A second principle, that of indeterminate design, is defined and differentiated from functionalist theory.