This paper proposes Foundation Model Transparency Reports (FMTRs) to enhance transparency in the development and deployment of foundation models. Drawing on the transparency reporting practices of social media platforms, we identify six design principles for FMTRs, including centralization, structure, contextualization, independent specification, standardization, and methodologies. We also align our design with existing government policies, such as the EU AI Act and the US Executive Order on AI, to show how FMTRs could improve compliance and reduce regulatory burdens. Our FMTRs are structured to provide standardized, comparable information about foundation models, including upstream resources, model properties, and downstream use. We also provide examples of how developers may report information related to these indicators. While current transparency requirements in government policies are often vague and not specific enough, our FMTRs aim to provide a more comprehensive and detailed framework for transparency. We also highlight the importance of contextualization and methodological clarity in transparency reporting. Finally, we discuss the challenges and benefits of transparency reporting for foundation models, including the potential for increased public trust and accountability.This paper proposes Foundation Model Transparency Reports (FMTRs) to enhance transparency in the development and deployment of foundation models. Drawing on the transparency reporting practices of social media platforms, we identify six design principles for FMTRs, including centralization, structure, contextualization, independent specification, standardization, and methodologies. We also align our design with existing government policies, such as the EU AI Act and the US Executive Order on AI, to show how FMTRs could improve compliance and reduce regulatory burdens. Our FMTRs are structured to provide standardized, comparable information about foundation models, including upstream resources, model properties, and downstream use. We also provide examples of how developers may report information related to these indicators. While current transparency requirements in government policies are often vague and not specific enough, our FMTRs aim to provide a more comprehensive and detailed framework for transparency. We also highlight the importance of contextualization and methodological clarity in transparency reporting. Finally, we discuss the challenges and benefits of transparency reporting for foundation models, including the potential for increased public trust and accountability.