While nonfinancial key performance indicators have recently gained importance in corporate reporting, their preparation process for management reports has remained a black box . Based on interviews with experts from various areas and hierarchical levels, the study empirically analyzes preparation processes in three publicly listed and four privately held German firms. The findings provide detailed insights into phases of preparation processes. Moreover, the promotor model is applied to determine the roles and communication of process participants. In addition, several internal and external factors influencing the process design are discussed using organizational theories. The findings of this study offer several implications for academics and stakeholders such as preparers or regulators.