The Bond grindability testing procedure has been standardized to obtain the same grindability values, i.e., Bond work index (BWi), on the same ore when tests are performed in different laboratories or by different operators. This is accomplished by the standardization of mill dimensions, tumbling speed, grinding-ball charge weight and distribution, sample charge weight in the mill and operating practice. The results of this investigation reveal that the Bond work index grindability values may differ substantially with different standard Bond ball mills. This paper reviews the results of this investigation.