PrefaceThe government uses all kinds of policy instruments to intervene in the economic process. The standard reason given for government intervention is market failure due to so-called external effects. If the external effects are positive, the market tends towards under-investment or underproduction compared with the social optimum. With negative external effects the result is precisely the opposite, namely over-investment or overproduction. For example, investment in R&D is characterised by knowledge 'leakage' to competitors who profit from it without having to pay for it. If the government wants to prevent under-investment in R&D, then it must provide subsidies to compensate for these 'leakage' effects. Looked at from the other direction, the theory of prosperity says that tax should be levied in the case of negative external effects.This study shows that well-intentioned public policy can have unintended (and unnoticed) side effects on the environment. Scientists, policy-makers and the public at large seem insufficiently aware of this problem.This report has been compiled in response to the request from the Minister of Housing, Spatial Planning and the Environment for a methodological study of the environmental effects of policy measures in the Netherlands. The study has produced a scientific method for charting first order environmental effects in a transparent, rapid and flexible way. Application of the method to a number of subsidies in the energy, agriculture, transport, and tourism sectors shows that there can be significant first order effects on the environment. In principle the method can be applied more broadly, e.g. for questions relating to the lack of a public policy. As long as it is applied responsibly the method is a useful aid for policymakers.