Nearly all software products have rigid and predefined interfaces. Users are usually unable to modify or customize features beyond cosmetic aspects. Interface adaptability is important because aspects such as user preferences and task sequences vary widely in engineering, even within specialized domains. A methodology for the creation of adaptable user interfaces using model composition is presented in this paper. User interfaces are generated dynamically through the composition of model fragments that are stored in a fragment library. When fragments are linked to models of physical behavior, interface model composition applications are likely to be easier to extend and maintain than traditional graphical user interfaces. A prototype system within the domain of bridge diagnosis illustrates the potential for practical applications.