Human social life is fundamentally structured by membership in different groups. Group membership tends to increase cooperation within groups but may undermine cooperation across group boundaries. This is critical because many of today’s biggest challenges — such as climate change — require cooperation beyond group boundaries. In preregistered laboratory experiments (planned N ∼ 800), we study whether groups are able to cooperate successfully when the provision of a public good depends on contributions from out-group members. To investigate inter-group cooperation, groups of six participants, in some treatments consisting of two subgroups of three, play a repeated threshold public goods game. To explain differences in contributions, we elicit social preferences, personal norms, social expectations, and contribution strategies conditional on others’ contributions. To examine how group identity shapes inter-group cooperation, we will vary group identity salience from absent to minimal to real national identities. Additionally, we aim to investigate whether emphasizing perceived commonalities or differences with out-group members facilitates or hinders cooperation.