Why and how do candidates choose the issues on which their campaigns are based? Drawing on a large database of candidate advertisements from the 1998 House and Senate campaigns, extant theories of issue emphasis, which focus on factors such as party ownership and candidate record, are tested here and these theories are expanded by examining in more detail the role of constituency characteristics. Most notably, party ownership's impact is demonstrated to be weak: candidates are more willing to ‘trespass’ or talk about the other party's issues than previous literature has found. Also ‘trespassing’ is shown to be facilitated by framing the other party's issues in certain ways. The results have implications for theories of candidate strategy and for normative questions, such as how much ‘dialogue’ occurs in campaigns.