Issue ownership theory is a tale of two actors. On the one hand, it theorizes how parties compete with each other in their struggle for votes. On the other hand, issue ownership isabout the citizen. It claims that voters are more likely to support a party if they think it is competent to handle issues they care about.This book provides unique insights into the undertheorized and understudied links betweenparty competence and the vote. It argues that issue ownership voting (or competence-based voting) consists of three assumptions: First, voters are primarily interested in havingissues handled by a competent party. Unlike in other issue voting models this impliesthat voters are reluctant (or unable) to deal with the specificities of the exact solutionto a political problem. Though positional considerations feed into evaluations of partycompetence, other factors are important, too. This is reflected by the second assumption, following which issue handling competence is a subjective preference with various sources.Third, competence is more decisive in the decision-making process if the voter cares deeplyabout the issue. These three assumptions yield the key formula of issue ownership voting:Voters support the most competent party on the most important issue.