QECBs are taxable bonds issued by state or local governments that finance energy conservation projects. The federal government subsidizes QECBs through tax credits or direct payments equal to 70% of the applicable tax rate. QECBs must be issued for qualified conservation purposes and proceeds spent on eligible projects within three years. Issuers must comply with various IRS rules both at issuance and over the life of the bonds to maintain the federal subsidy.