A municipal bond's tax exemption is not a permanent attribute of the bond. It is a conclusion that depends on how the financed facility is used for as long as the bonds are outstanding, and a lease signed years after closing can destroy it retroactively. This article explains that structure — the private business use and private payment tests, the arbitrage and rebate rules, and the remedial actions available when something goes wrong. It then covers the disclosure regime that applies despite the securities exemption, the antifraud framework and its limits on secondary actors, and the continuing obligations that outlive everyone who worked on the transaction.