The MSRB "makes rules regulating dealers who deal in municipal bonds, municipal notes, and other municipal securities," as explained by the MSRB Web site (www.msrb.org/). The site feature's the MSRB's rules, reports, forms, addresses and phone numbers, and the MSRB's User's Manual for Customer Transaction Reporting, which details the rules dealers have to follow to report their municipal securities trades to the MSRB.
Most MSRB materials are also available in CCH's Municipal Securities Rulemaking Board Manual.
Filings: Official Statements and other MSRB filings are discussed in the "Municipal Bonds" entry.