Book excerpt: The world trade of plants and plant products is gradually increasing in both quantity and variety. Also, as more and more citizens are nowadays travelling to distant destinations, there is an increased risk of unintentionally importing harmful organisms and invasive species. Governments respond to increased phytosanitary risks by imposing trade-restricting measures. However, they are under increasing pressure of the private sector and the World Trade Organization to justify costly and trade-restricting phytosanitary policies. On the other side, current phytosanitary policies are required to account for impacts on the environment. This book presents a number of recent scientific developments regarding the economic analysis of impacts that harmful organisms have on agriculture and the environment, and of measures to control these organisms. It also contains a number of new approaches that integrate economic and epidemiological modelling and economic approaches for measuring these impacts.