As a result of rapid advances in molecular genetics, diagnostic capabilities in clinical genetics are also rapidly increasing. One of the most significant characteristics of the new genetics is the extension of options for predictive genetic testing from 'classic' and relatively rare hereditary disorders to common diseases like cancer (Marx 1991; Grody 1994; Nowak 1994a; Smith 1996). This development is generally seen as a major challenge to existing health care systems and to the organization of clinical genetics services in particular (Harris and Harris 1995; Julian-Reynier 1996). In this chapter we focus on cancer genetics as a field in which the extension of options for genetic testing is already clearly visible and which thus allows us to study the implications of this development on an empirical level.