Users of interactive computer systems will typically display a wide range of computing experience, a fact which is rarely taken into account when user interfaces are constructed. The difficulties encountered by users using a rigid user interface are highlighted, and the role of adaptable user interfaces in the process of improving user-computer interaction is outlined. Particular emphasis is placed on multi-level user interfaces, where each level of the interface is intended to satisfy the needs of a specific class of user. Consideration is given to the use of multi-level interfaces in encouraging users to advance to higher experience levels as their knowledge grows. The difficulties presented during implementation of such complex interfaces are highlighted and a methodology for the specification and design of interactive systems and their user interfaces which encourages the use of sophisticated user-computer interaction is described. A prototype Dialogue Development System has been produced which supports the use of this methodology with the Ada* programming language. The appropriateness of this approach to programming interactive systems in Ada and other languages is discussed.