Accurate atmospheric measurements of ice nucleating particles (INPs) are needed for improving understanding of their role in affecting cloud properties and climate. Prior international workshops on comparing INP measuring systems were conducted mainly in the laboratory, where high concentrations of INPs were typically employed. This workshop established a template for the conduct of comparisons in an atmospheric setting where low number concentrations of INPs typically exist, representing a very small fraction of all particles. Overall, this study stimulates advances of important but challenging INP measurements and strengthens confidence in their use to understand ice formation in clouds.