Parties campaign on a range of topics to attract diverse support. Little research, however, looks at why parties narrow or expand the scope of their campaign or shift attention across issues. Focusing only on a single dimension or topic may lead scholars to estimate wrongly the magnitude of the effect of parties’ experiences in a government or economic context. I propose that electoral conditions influence the scope of parties’ manifestos. I test hypotheses using a measure of issue diversity: the Effective Number of Manifesto Issues (ENMI). Based on analysis of 1662 manifestos in 24 OECD countries from 1951 to 2010, the results support the theory. Government parties have higher ENMI. Opposition parties and governments expecting a reward for the economy limit their issue appeals. Tests of the underlying mechanism using data on issue dimensions and policy data provide additional support. These findings have important implications for the study of election strategy and democratic accountability.