The vulnerability of a given system corresponds to its susceptibility to be harmed, reflecting its inability to cope with adverse effects. This inability is the consequence of three key parameters that are interconnected, the sensitivity, the exposure and the adaptive capacity of the system in front of adverse effect. At the farming systems scale, some authors tried to understand links between sensitivity, exposure, while others focused on a conceptual analysis of adaptive capacity without proposing a quantification of the level of vulnerability. Other authors propose a measurement of vulnerability based on the evaluation of farming systems characteristics, as if the factors explaining vulnerability where yet known. In this paper, we first propose quantitative indicators for the three key parameters of vulnerability. Then, we apply our framework to mixed crop-livestock systems and we show that various levels of vulnerability should be explained by both some characteristics of the systems and strategies of farmers. Low vulnerable systems are more diversified, with one additional production unit and significantly higher sales of transformed products on average (+1.5 points of percentage in comparison with moderate vulnerable systems). A lower dependency to markets through better feed management (lower stocking rate) and a higher efficiency in energy and water consumption are also key determinants of low vulnerability. This management permits having bigger farms (+43 to 20 hectares) and higher flock sizes (+13 livestock units on average). The ability to cope with adverse effect is not significantly different between stable, non-stable, flexible and rigid farming systems. Our findings are a first step toward a better understanding of farming systems vulnerability: their validation on another sample would help contributing to the conception of innovative farming systems in research and to better advices for vulnerable farmers in operational projects.