The aim of this chapter is to formulate theoretical foundations for deferring the IS design process to inform adaptable usage of deferred systems. A research agenda for Deferred System’s Design is set and a new system component, the System-System Environment Interface, is defined as the public interface through which a deferred system can maintain close coupling with the system environment. A Problem-solving and planning technique is suggested, the Deferred-Specified IT/IS Matrix, to aid software developers to position a proposed system development in the system environment. A systems analysis technique is suggested to identify deferment points in a given system design. The chapter identifies seven properties of deferred systems that software developers can use to inform adaptable system designs.