Although the motives for China’s development of the Belt and Road Initiative have been well studied, scholars have yet to examine why partner states seek to join. This paper seeks to fill this gap by focusing on the memorandums of understanding (MOUs) that states sign with China to formally join BRI. Based on our analysis of these MOUs, we argue that, overall, the costs for joining the BRI are low but the potential benefits are high. Thus, most states should join the BRI unless they view the costs as higher or the benefits as lower. Specifically, we suggest that democracies and states with close security ties to the United States should be less likely to join because they view joining a Chinese-led initiative as more costly. Our statistical analysis using a new dataset of BRI MOUs and two paired case studies provide empirical support for this argument.