What do a large corporation with extra cash on a Tuesday, a bank that needs reserves overnight, and the U.S. Treasury issuing a one‑month IOU have in common? They all turn to the money market — the global network where cash is borrowed and lent for hours, days, or a few months at a time. This chapter shows you the instruments and institutions that make this lightning‑fast world of short‑term funding work, and why it matters for every corner of finance.