This chapter addresses a major gap in current understanding of issue ownership. While the existing literature offers ideas about what may cause ownership change, and some examination of isolated cases, there has - until now - been no systematic test of why parties lose and gain issue ownership. The authors provide such a test in this chapter, providing cross-national over-time evidence in support of a theory of issue ownership change. The theory argues that ownership change should occur when something happens that is so clear a signal, and so symbolic, that widely held beliefs about political parties are thrown into question. Either a major performance shock or a major symbolic policy change should take place, and there should be party supply to compete on the issue. Conditions associated with 37 changes in issue ownership in the U.S., U.K., Australia and Germany are analysed, alongside cases of no-ownership-change, enabling the authors to show that in all cases of issue ownership change there are pre-conditions of public and/or political salience, the presence of a symbolic performance shock or change, and the presence of a symbolic policy shift by a party. The simultaneous presence of those conditions is not observed in cases of ownership stability - for seven issues over 58 separate election cycles – providing further evidence for the theory.