Policy evaluation research has traditionally favored quantitative approaches. These quantitative techniques can be based (i) on econometric analyses to infer the causality chain triggered by the implementation of a policy or; (ii) be based on a control-treatment approach based on the selection of the best possible counterfactual in order to capture the impact of a policy on a target variable. However, such quantitative approaches have difficulties into integrating qualitative dynamics -such as the influence of governance and institutions- and understand the intertwined and complex nature of interactions between SES variables affected by those policies. As a result, purely quantitative policy evaluation is not able to capture cascade effects and non-linear interactions between primary and secondary system variables. This introduction discusses how to identify the system variables of interest, its interactions and the combination of methods to describe them. (Texte intégral)