This work contributes a physical synthesis model of the trombone, a virtual musical instrument emphasizing quality sound production, and interactivity. The focus is on modeling and coupling four parts of the trombone: the instrument bore, the bell, the vibrating lips, and the mouthpiece. The model of the instrument is made parametrically flexible by using a combination of filter elements modeled either using known theory or, for elements not well described theoretically, from acoustic measurement. In particular, acoustic accuracy of the bell reflection and transmission is explored by comparing results obtained from measurement, to those obtained from a piecewise conical model. In addition, the playability and performance characteristics of the complete sounding model—when coupled to a mouthpiece and a configurable generalized reed model—is discussed with reference to expected acoustic behavior.