Following the need identified by the ISPE survey of compounding pharmacies and regulators, it is evident that compounding pharmacies would benefit from consolidating FDA regulations and recommendations and the United States Pharmacopeia (USP) criteria into a single guide. The ISPE Guide: 503A Compounding – Regulatory Basis and Industry Good Practices for Pharmacies provides an overview of FDA regulations and guidance necessary for conducting safe compounding to help pharmacies understand the requirements of FD&C Act Section 503A. In addition, the ISPE Guide outlines the authority of State Boards of Pharmacy and their coordination of oversight with the FDA. A significant portion of the Guide addresses USP Chapters <795>, <797>, <800>, and <1163>, which are critical for the operation of 503A pharmacies. The differences in USP <795> for nonsterile compounded preparations and USP <797> for sterile preparations are discussed throughout this ISPE Guide to aid 503A compounders in understanding the requirements and accessing appropriate information. Discussions include general compounding requirements for 503A pharmacies focusing on the Quality system and its application throughout the process from incoming materials and facilities and equipment, to storage, shipping, and transport. Readers will find the information on personnel knowledge and training requirements valuable. To aid pharmacies in maintaining compliance with federal and state regulations, several lists of suggested Standard Operating Procedures (SOPs) based on the type of compounding conducted are included. Although a high-level overview of the state board of pharmacy model is provided, the rules of the State Boards of Pharmacy and other equivalent state regulatory groups are considered out of scope, given the multitude of individual state regulations.