An ISPE survey of compounding pharmacies and regulators overwhelmingly demonstrated that 503B outsourcing facilities could benefit from comprehensive guidance summarizing regulatory requirements. The ISPE Guide: 503B Compounding – Regulatory Basis and Industry Good Practices for Outsourcing Facilities aims to help facilities understand the FD&C Act Section 503B requirements. This ISPE Guide combines FDA regulations and recommendations with pharmaceutical industry standards, providing a go-to document for any size 503B facility. The compounding process is covered, from the importance of CGMPs to establishing a Quality system (including qualifying suppliers and vendors), receipt of raw materials/active ingredients, and shipping of the finished drug product. Along with facility and equipment design recommendations used in traditional aseptic manufacturing and scaled to meet the needs of 503B facilities, the Guide presents industry good practices for aseptic manufacturing including information on personnel training and qualification. Verifying the suitability of compendial methods and validating non-compendial methods are discussed for both microbiological and analytical testing. An explanation of beyond-use dating and applicability of limited stability testing is provided, along with stability best practices. Readers will find the chapter on what to expect in an inspection a useful aid in preparing for regulatory inspections. Although a high-level overview of the state board of pharmacy model is provided, the details on the rules of the State Board of Pharmacy and other equivalent state regulatory groups are out of scope given the multitude of individual state regulations.