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 this writing group to report on the need for guidelines for use of CFD in single phase nuclear reactor safety (NRS) applications. CSNI approved a writing group at the end of 2002, and work began in March 2003. A final report was submitted to the Working Group on the Analysis and Management of Accidents (WGAMA) in September 2004, summarising existing best practice guidelines (BPG) for CFD, and recommending creation of a BPG document for nuclear reactor safety (NRS) applications. This action was approved by the WGAMA and the CSNI, resulting in the creation of this document. Though not meant to be comprehensive, this document is intended to provide an internally complete set of guidelines for a range of single phase applications of CFD to NRS problems.