I provide the first systematic analysis of collateral choices in one of the main short-term funding markets, the repurchase agreement (repo) market. Repos establish a natural connection between short-term and long-term funding markets as long-term bonds serve as collateral in short-term funding trades. In general collateral repos, banks can choose which bond they post as collateral out of a predefined list. In the aggregate, on-the-run bonds are more likely to be delivered than cheapest-to-post securities, which is surprising given that the former are more expensive. I rationalize those findings in a theoretical framework that links the repo to the bond market. My results are relevant for explaining bond market patterns that are different in the United States compared to the euro area.