AbstractI study the impact of party campaigns on tactical voting, focusing on voters with tactical incentives. Focusing on three UK Elections, I exploit panel data within each election to address endogeneity in party behavior, which would otherwise bias the estimates of campaign effects. My findings show that party contacts during campaigns have an influence in encouraging loyalty to preferred nonviable parties and defection to alternative viable ones. These findings are important as relatively little is known about what influences voters’ decision to cast tactical votes, beyond their demographic characteristics and the electoral circumstances they may find themselves in.