Against a background of growing concern with environmental issues, resource consumption and waste production in the construction sector, this article presents the results of a study on the implementation of environmental management systems (EMS) certification in Portuguese construction companies. It reports on how construction companies perceive motives, difficulties, benefits and effectiveness of implementing EMS certification. A questionnaire served as the basis for data collection. It was sent to all certified construction companies listed in the IPAC (Portuguese Accreditation Institute). Results show that reasons for companies to use environmental certification go beyond legislated environmental requirements. Although some differences can be noted between large and small companies, certification is regarded as a process in which the benefits outweigh the costs, particularly in relation to increased recycling of raw materials. There are significant difficulties in the availability of human and financial resources, mainly in smaller companies. The main factors to ensure effectiveness of environmental certification are the commitment and support of top management, the establishment of clear environmental objectives consistent with environmental policy, training, time availability and raising awareness among all employees.