Despite its wide use in port studies, the concept of port system remains relatively vague and ill-defined, ranging from a geographic or administrative area containing two or more ports to an interconnected set of port nodes in a given network. Based on a corpus of no less than 268 articles, this chapter investigates how port systems have been studied since the pioneer works of the 1960s. The bibliometric approach underlines a growing publication trend and collaboration dynamic over time, a shift from geography to transport journals, and a widening focus from national to transnational and global. The content analysis reveals that although more than half of the corpus concerns issues of concentration/deconcentration, new concepts are emerging in port system studies, which underline different spatial patterns and processes. To be noticed is the growing importance of maritime connectivity, after decades of dominant land-based models focusing on hinterlands.