In this paper, the concept of environmental indicator is reviewed as a relevant element used in the environmental management of any organisation. The importance of this element within an Environmental Management System (EMS) is also justified. Although EMS standards recognise the relevance of using indicators, they do not specify any methodology to identify which indicators have to be implemented. In addition, the present research demonstrates that although there is a high percentage of European ports that have already implemented performance indicators, most of them do not mention the method applied to obtain the indicators. This suggests that some of the procedures used by ports to identify indicators may not necessarily be science-based or systematic in approach. For these reasons, the need to develop a new methodology able to identify the ports' most adequate indicators was detected. Therefore, a Tool for the identification and implementation of Environmental Indicators in Ports (TEIP) was developed. It aims at identifying performance indicators in ports and providing guidelines for their proper implementation. This is a computer and science-based tool (www.eports.cat/teip) that provides a quick calculation and outputs, and it is designed to be as user-friendly and practical as possible in order to facilitate its completion by the user. This new methodology is applicable to all types of ports no matter the size, geographical location or its commercial profile; it provides targeted and specific results for each one. TEIP aims at helping port managers at easily determining their significant port indicators, which provides valuable elements for the decision-making processes.