In environmental cases, The Swedish Land and Environmental courts have not only to consider environmental interests but also economic interests. The overall aim is to achieve both a good environment and maintain an industry that generates jobs and contributes to welfare. The dissertation focuses on the intersection between environmental interests and economic ones in legal decision-making, especially in relation to how the Proportionality principle contained in Chapter 2, Section 7 of the Environmental Code is applied. The principle states that general rules of consideration (including the precautionary principle) must be reasonable. For example, the precautionary principle should be both environmentally justifiable and financially reasonable when the principle is applied. The dissertation examines the legal balancing of interests, between economic and environmental interests, applying the concept of rationality. The concept of rationality is the core of the theoretical elements of the study, more precisely how Theodor Adorno and Max Horkheimer perceive rationality in Dialectic of Enlightenment. According to Adorno and Horkheimer, instrumental rationality is dominating. Although, rationality often legitimizes legal proceedings there has been little interest in how rational actions influence the results of legal processes. The dissertation questions the neutrality of the concept of rationality. A rational action may have an impact on court decisions. A main finding is the relation between instrumental rationality and economic actions. When judges are trying to be rational, they will favor economic interests. There is a bias towards economic interests in the underlying structure of the decision-making process. This has an impact on the way in which legal interests – specifically those between environmental interests and economic interests – are balanced. Legal decision-making is better suited for economic models than environmental processes. I miljöprövningarna har mark- och miljödomstolarna inte bara att ta hänsyn till miljöintressen utan även till ekonomiska intressen. Vi ska uppnå en god miljö och samtidigt ha kvar den industri som genererar jobb och bidrar till vår välfärd. Denna avhandling utgår från mötet mellan miljöintressen och ekonomiska intressen i mark- och miljödomstolarnas beslutsfattande. Fokus ligger på rimlighetsavvägningen i 2 kap. 7 § miljöbalken. Undersökningens huvudresultat är att miljöintressen missgynnas i själva beslutsstrukturen när dessa vägs mot ekonomiska intressen, detta genom att beslutsfattandet är bättre lämpat för ekonomi än miljö. Undersökningens teoretiska moment utgår från rationalitetsbegreppet och rationalitetssynen i Upplysningens dialektik av Theodor Adorno och Max Horkheimer. Rationalitet legitimerar beslutsfattandet samtidigt som rationalitet inte sällan ses som ett neutralt medel. Avhandlingen ifrågasätter rationalitetens neutralitet, ett rationellt handlande kan istället anses påverka själva beslutsfattandets resultat.