Over the last two decades an increasing volume of research has demonstrated the efficacy of constituency campaigns at British general elections, using a range of indicators. In general, the more intense a party's campaign in a constituency, relative to its opponents', the better its performance there. These conclusions have been reached using aggregate-level data, and are confirmed again here in respect of English constituencies at the 2001 election. In addition, however, the novel before-and-after design of the 2001 BES allows us to test for the impact of constituency campaigning at the level of the individual voter. Analyses of these data provide strong supporting evidence to the aggregate-level analyses: people who intended to vote for a party when the campaign started were more likely to do so if it contacted them during the campaign.