Online customer reviews are crucial to inform customers’ online purchase decisions. However, the complex nature and immense volume of customer reviews can easily overload customers’ cognitive resources, with significant negative consequences for customers and online shopping sites. In response, first online shopping sites provide summaries of textual review content (i.e., customer review summaries) alongside individual customer reviews. Building on cognitive load theory, this study examines how customer review summaries in textual and visual presentation formats affect customers’ cognitive load during online purchase decisions. With an incentive-compatible online experiment, we find that displaying customer review summaries reduces cognitive load. While textual and visual review summaries are equally effective, displaying both textual and visual review summaries reduces cognitive load the most. These findings contribute to literature on the design of customer review systems and provide relevant insights for practitioners on how to support customers’ online purchase decisions.