FINRA & the SROs
Self-regulatory organizations are industry bodies that regulate their own members under SEC oversight; FINRA is the SRO for broker-dealers, while the MSRB writes rules for the municipal securities market.
FINRA administers qualification exams (including the SIE), registers representatives, and disciplines members for rule violations. State regulators (coordinated through NASAA) enforce state blue-sky laws, and the Federal Reserve, FDIC, and Treasury round out the regulatory picture for banking-side activities.