This publication presents the results of an IAEA organized intercomparison exercise on codes used in the application of the. Neutron Activation Analysis (NAA) k0 method. NAA is the most common technique implemented in research reactors worldwide. It allows the determination of the elemental composition of samples weighing from micrograms to kilograms. The k0 method for NAA has greatly facilitated the implementation of NAA at new facilities. It allows for the determination of elemental mass fractions, together with their uncertainties, without the need for sample-matched reference materials. As a consequence, various software packages for the application of this method have been developed. In 2021, the IAEA initiated, an intercomparison exercise of k0 software packages, in which the software contributions to the uncertainty budget was determined. The developers of all known k0 software packages were invited to participate, and all but one of the invited packages were represented in the exercise, including the two widely available codes and three codes developed in particular institutes for their own purposes.