This research looks into the relationships between uncertainty, variability and flexibility in manufacturing systems from an operations strategy viewpoint. After reviewing the literature concerning the three categories, 6 research propositions are defined in order to guide the research. A research method (case-studies with semistructured interviews) is then selected and field research which encompassed 8 companies, including the ones of the pilot study is described. The field work resulted in 4 in-depth case studies, performed with Brazilian and British companies (2 in each country), all of them belonging to the automotive industry. Based on the conclusion i of the literature review and on the results of the field work, the 6 propositions are discussed and an original model is then proposed in order to help managers understand and analyze unplanned change from the operations management's viewpoint. The model proposes two complementary categories which are used by managers in order to deal with unplanned change: control and flexibility. Control is related to the managerial actions which aim to restrict the amount and level of unplanned change with which the organization will have to deal ex-ante the occurrence of the change. Flexibility is related to the managerial actions taken in order to respond to the uncontrolled unplanned change's effects ex-post the change. Types and dimensions of control and flexibility are proposed and discussed. A new way to look into the flexibility of the manufacturing structural resources is also proposed, which is based on the presence of the resource switchability and on some types of redundancy of the resources - of capacity, of capability and of utilization.