This paper summarises the development of monoclonal antibody (Mab)-based immunoassays measuring antibodies to non-structural proteins of FMDV to differentiate infection from vaccination. Of the three non-structural proteins 2C, 3C and 3ABC evaluated in this study, the polypeptide 3ABC was the most immunogenic. Three ELISAs for the detection of antibodies to 3ABC were developed. Two assays rely on the competition of test sera against either a anti-3A Mab or against antisera to 3ABC raised in rabbits and guinea-pigs. The third, 3ABC Mat-ELISA, based on the direct binding of antibodies to the 3ABC trapped by a specific Mab, provided the best combination of specificity and sensitivity. The 3ABC Mat-ELISA was extensively validated for cattle, either in experimental and in field conditions, showing specificity of 99% in vaccinated and in naive cattle and the capacity to detect silent infections in FMD-vaccinated populations. The test showed similar specificity and sensitivity in experimentally vaccinated and infected sheep.