This document represents the conceptual foundations of the EU-FP7 OPTIC project. As such, it seeks to provide a range of theoretical resources with which to develop an informed and pragmatic understanding of the complex causal processes involved in contemporary transport policy-making at the European level. Specifically, this deliverable aims to further methodological advancement with respect to the identification, classification, ex-ante prevention and ex-post mitigation of policies‘ unintended effects, and the systematic manner in which individual policy measures may be combined so as to improve their effectiveness, acceptability and feasibility. Overall, we argue that policy packaging can offer a far greater potential for achieving policy targets and objectives than single policy measures deployed in isolation. Yet, a careful and relatively well designed process must be undertaken for such packages to be effective.