Abstract: The role of NAA in the metrology of modern inorganic trace analysis is to be discussed in a series of three papers, beginning from this one. They are:1)the qualification of relative NAA as a primary method of measurement; 2) the unique function of parametric NAA as a "back-up" method of relative NAA; and 3) the role of NAA in the characterization of a new generation CRMs suitable for quality control of microanalysis. The first of the series, the principle, the unceratinties and the traceability of NAA are analyzed. The qualification of NAA at the state of the art level as a primary ratio method is thus justified. An example is given to further verify the position of NAA as a primary ratio method. Advantages and drawbacks, as well as current status and future perspectives, of NAA as a primary method are discussed. Definitions of relevant terms and international norms are attached as appendices for the convenience of the reader.