README: This is the project page for Isler, O., Gächter, S., Maule, A.J., Starmer, C., 2021. Contextualised strong reciprocity explains selfless cooperation despite selfish intuitions and weak social heuristics. Scientific Reports 11, 13868. [https://doi.org/10.1038/s41598-021-93412-4][1] The project involves two experiments. The preregistration for the experiments can be found by clicking “Registrations” above. In addition, the project folder below includes five files: two documents including the experimental materials (PDF files), the raw data file (Excel file), the analysis data file (Stata data file), and the analysis code file (Stata do file). The raw data file presents all variables, elicited during the studies and used in the analyses, in an anonymous way. The analysis data file includes additional variables elicited by running Part A of the analysis code in Stata. Parts B and C of the analysis code automatically run all of the analyses presented in the paper and its supplement. This work was supported by the European Research Council [Grant Number [ERC-AdG 295707 COOPERATION\] ][2]and the Economic and Social Research Council [Grant Numbers ES/K002201/1 and ES/P008976/1]. [1]: https://doi.org/10.1038/s41598-021-93412-4 [2]: https://www.nottingham.ac.uk/cedex/erc-project-cooperation/home.aspx