The Nkomati ore body, situated in the Mpumalanga Province, in South Africa, is an extensive Nickel/Copper reserve being investigated by the Nkomati Joint Venture. The extraction route for the Main Mineralised Zone of the ore body is currently being investigated. This paper describes the milling circuit selection procedure for the Main Plant concentrator. The selection of the Nkomati Main Plant concentrator milling circuit followed a rigorous procedure. A key aspect in the circuit selection process was the close interaction between the relevant disciplines : Geology, Mineralogy, Mining and Metallurgical. The comprehensive circuit selection procedure based on a milling rate of 300 000 tons per month will be described, from the complete set of pilot and bench-scale results, the design criteria, the mineralogical factors and the Nkomati project philosophies, through to the final decisions on the circuit configuration and mill sizings. The proposed circuit for the 300 000 tpm Nkomati Main plant would be one of the largest milling installations in the world. The proposed circuit incorporates one of the largest primary FAG mills, and the largest secondary pebble mill. A critical aspect in the circuit selection procedure was the various means employed to reduce the very real risks associated with an operation of this size.