Abstraction is key to model construction for simulation. While traditionally considered to be a black art, the importance of methodological support for abstraction is becoming increasingly evident. Complex distributed simulation systems, supporting multiresolution model sharing, presuppose effective ways to develop and correlate the underlying abstractions. Although a conceptual and computational framework grounded in mathematical systems theory has been around for some time, discussions of abstraction issues still often proceed through individual anecdotal experiences with little cumulative impact. This paper reviews theory and concepts available for working with abstraction in model construction.