Sequencing flexibility refers to the possibility of interchanging the order in which required manufacturing operations are performed. In this paper, we address several issues related to the modelling, measurement and performance evaluation of this flexibility in manufacturing systems. In particular, we introduce several representation and measurement schemes for sequencing flexibility and discuss the usefulness and limitations each. We then propose a new performance-based approach for quantifying the value of flexibility. To this effect, we study the relationship between flexibility and system performance under a variety of design assumptions and operating conditions. These relationships are used to identify key characteristics of a measure of flexibility that is reflective of system performance. This measure is to allow system designers and managers to predict performance based on existing levels of flexibility and/or determine the amount of flexibility required to achieve a certain level of performance. This measure is shown to be easier to calculate than traditional performance measures and to be possible to use as a substitute for these measures in estimating the effect of flexibility on performance.