This Water Quality Trading Toolkit for Permit Writers (Toolkit) is intended to facilitate trading by providing NPDES permitting authorities with the tools they need to facilitate trading and to authorize and incorporate trading in NPDES permits. Although the Toolkit primarily targets state, tribal and EPA NPDES permitting authorities, it might also be useful to other stakeholders interested in water quality trading and the NPDES permitting process. Users of the Toolkit should have an existing, fundamental understanding of both water quality trading concepts and the NPDES permitting process. To ensure consistency and minimize redundancy, the Toolkit refers users to existing EPA guidance on water quality trading and NPDES permit development and issuance whenever possible. This guidance is based on EPA's Water Quality Trading Policy (Trading Policy) published in January 2003. The Trading Policy was written on the assumption that, if a total maximum daily load (TMDL) were in place, all trading partners would be covered by the TMDL. In this case, wasteload allocations (WLAs) and load allocations (LAs) under the TMDL form the baseline for trading. In all cases, permits must be designed to meet water quality standards as required under Clean Water Act (CWA) section 301(b)(1)(C). Inclusion of trading provisions in NPDES permits should facilitate meeting this requirement.