This chapter proposes an analysis of worldwide inter-port shipping flows from a strength clustering perspective. A diversity of factors seems to explain the formation of clusters: geographic proximity among closely located ports (i.e. maritime regions), trade proximity (corridors) and historical path-dependency (long-term ties) among more distant ports. Since those factors are not directly tested, this chapter paves the way for further research on the geographic and economic relevance of clusters in the network analysis of shipping flows.