This paper has as main objective to propose the economy of the sea as a (regional) development policy in “maritime countries” by nature. To this end, we begin by analyzing the evolution of the economy of the sea concept, understood as an analytical tool that can play the role of strategic (regional) development policy. To make it possible, we analyzed the cluster theory (maritime), highlighting particularities of its governance, nature, and performance. We then narrow the dialogue between the theoretical framework and regional development, presenting some key variables that can contribute to the analysis and evaluation of different cases of maritime clusters, suggesting it as a model to make such a development policy feasible. Taking the case of two maritime clusters in Brazil (Rio Grande, and Rio de Janeiro), we create and analyze the Herfindahl-Hirschman index (HHI) based on the number of employees of the municipalities facing the sea using official data of the Annual List of Social Information (RAIS), having as base year 2018. This proxy may be used as a guide to promoting both clusters, evaluating the current scenario and, at the same time, indicating potential sectors to be developed or encouraged in both cases. Through this economy of the sea perspective, the sea can be explored, needs to be managed and must be protected.