Evidence use is widely acknowledged as essential for crafting effective public policies. However, despite its critical role, we know surprisingly little about the specific sources of evidence that inform policy documents globally. This paper explores the role of evidence in policymaking by examining the sources that shape policy documents across 190 countries. Using a dataset of over 10 million policy documents, we analyze the types of evidence drawn upon by governments, focusing on contributions from academic research, knowledge brokers such as think tanks, international organizations, and foreign governments. Through a combination of quantitative and network analyses, we map patterns in the use of these sources, highlighting regional and political variations, and identifying key trends in the evolution of evidence-based policymaking. Our findings reveal differences in the reliance on domestic versus international evidence, while also exploring the influence of political systems and geography on evidence use.