Various open probability-based panel infrastructures have been established in recent years, allowing researchers to collect high-quality survey data. In this report, we describe the processes and deliverables of setting up the GESIS Panel, the first probability-based mixed-mode panel infrastructure in Germany open for data collection to the academic research community. The reference population for the GESIS Panel is the German-speaking population aged between 18 and 70 years permanently residing in Germany. In 2013, approximately 5,000 panelists had been recruited from a random sample drawn from municipal population registers. We describe the outcomes of the sampling strategy and the multistep recruitment process, involving computer-aided personal interviews conducted at respondents’ homes. Next, we describe the outcomes of the two self-administered survey modes (online and paper-and-pencil) of the GESIS Panel used for the initial profile survey and all subsequent bimonthly data collection waves. Across all stages of setting up the GESIS Panel, we report sample composition discrepancies for key demographic variables between the GESIS Panel and established benchmark surveys. Overall, the findings highlight the usefulness of pursuing a mixed-mode strategy when building a probability-based panel infrastructure in Germany.