Glycated hemoglobin (HbA1c) is considered the gold standard for monitoring and the treatment of diabetes. After the success of the DCCT and UKPDS studies, which showed that HbA1c is an independent indicator for risk of developing chronic complications of diabetes, intensive work began on the standardization of this parameter. Currently, the process of standardization of HbA1c determination is being pursued by two independent international organizations: NGSP and IFCC. At present most HbA1c determinations carried out worldwide are done via a test which is performed using uniform and standardized methods, which have been certified by the NGSP. At the same time, the IFCC has created a new, more consistent and specific method of standardization, but this method is not used routinely. According to the IFCC standard, HbA1c values are significantly lower compared to the results obtained by NGSP. Moreover, the IFCC has introduced a new alternative unit of HbA1c mmol/mol. Discrepancies between the programs of the two organizations, their advantages and disadvantages, have led to the consensus on global standardization of HbA1c determinations. This paper presents aspects of the standardization of HbA1c determination methods, which takes into account the obtained values and recommended range of values for each group of diabetic patients, as well as the statement of the largest diabetological organization.