During the last 30 years, environmental issues have become very important for governments, consumers and companies. Firms, aware of their environmental responsibilities, have started to show an important commitment to society and the natural environment, developing environmentally friendly strategies. However, the factors that determine the choice of environmental strategies are still unclear. They range from ethical motivations to social, legislative and competitive factors. This study analyses the main antecedents that influence firms' ecological behaviour, distinguishing between environmental orientation and environmental strategies. The hypotheses proposed in this study are analysed by means of a structural equation model on a sample of 235 industrial firms. The results reveal that competitive motivations and management commitment are the most important factors explaining why firms incorporate environmental issues into their strategic planning process. Moreover, management commitment is a critical factor for firms because managers' per-ception about customers' ecological concern directly influences firms' environmental behaviour.