In May 2002, an “Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems” was held in Aix-en-Provence, France. One of three recommended actions was the formation of a writing group to report on the need for guidelines for use of CFD in single-phase nuclear reactor safety (NRS) applications. The Committee on the Safety of Nuclear Installations (CSNI) approved the writing group at the end of 2002, and work began in March 2003. A final report was submitted to the Working Group on Accident Management and Analysis (WGAMA) in September 2004, summarising existing best practice guidelines (BPG) for CFD, and recommending creation of a BPG document for NRS applications. This action was approved by WGAMA and CSNI, resulting in the creation of this document.