This paper describes the work used to develop and validate the BrandBuilder loyalty model. Evidence of the usefulness and validity of three measures of loyalty will be presented: -1 behaviourally-based measures of loyalty to the brand; -2 attitudinally-based measures of loyalty to the brand; and -3 loyalty to individual product categories. Results of a large-scale study in which the attitudes and behaviour of thousands of consumers were measured will be presented. Evidence of the models ability to forecast a brands health over time will be offered based on this data. Data will also be shown for a number of different product categories and comparisons will be made between the five major European markets (United Kingdom Germany France Italy and Spain) and the United States. Finally conclusions will be drawn about the characteristics of categories and countries which possess higher vs. lower proportions of loyal buyers of brands.