The current container terminal market is facing challenging and uncertain times. Terminals must increase their handling capacity, efficiency, and productivity to remain relevant in a highly competitive market. There is growing concern about terminal operations’ local and global environmental impact. Regulations force terminals to adopt more sustainable, greener alternatives for handling operations. Thus, terminals face the double challenge of making their operations greener while maintaining or enhancing productivity and efficiency. This chapter is the first part of a two-part study addressing the greening potential of container terminal clusters to reduce their environmental impact during operations. This chapter aims to provide a set of factors that enables the clustering of terminals considering their greening capabilities. The factors identified in this chapter all have a direct or indirect link to the greening capabilities of a terminal environment. A literature review is performed to identify these factors. At the end of the chapter, the factors are utilized for a set of container terminals in a group of European seaports participating in the PIONEERS project. This project demonstrates 19 different innovations that aid ports in reducing their environmental impact. Nine factors are identified: equipment, level of terminal automation, spatial dimensions (yard layout, terminal size, yard capacity, and quay length), geographical location, port and terminal governance structure, throughput, and available energy sources. Each of these factors is further classified into sub-classes. Terminals with similar factors can be clustered together.