Why are some parties more likely than others to keep the promises they made during previous election campaigns? This study provides the first comparative analysis that addresses this question with common definitions of pledges and fulfillment. We study the fulfillment of 18,743 pledges made in 54 election campaigns in 12 countries. We find high levels of pledge fulfillment for most parties that enter the government executive, and substantially lower levels for parties that do not. The findings challenge the common view of parties as promise breakers. The degree to which governing parties share power affects pledge fulfillment, with parties in single-party executives, both with and without legislative majorities, having the highest fulfillment rates. Within coalition governments, the likelihood of pledge fulfillment depends on whether the party receives the chief executive post and whether another governing party made a similar pledge, but not on the ideological range of the coalition.