The NFA's Forex Transactions: A Regulatory Guide" is a comprehensive source for all rules and regulations regarding forex. In addition to this guide, you should also consistently monitor the NFA Forex Compliance page for an rules, resources, interpretive notices, or notices to members updates. It is also helpful to sign up for NFA and CFTC email updates (which can be done on the NFA and CFTC homepages) for consistent updates and press releases relating to forex.
