This paper aims at discussing how to contribute to sustainable development by targeting underbanked market segments: according to a common view, they include people who have become blacklisted by major banks, are young consumers, want to avoid debt collectors, are fed-up with fees, are out of a job or had a bad customer experience; in these cases, traditional financial services could—or would—be hardly accessed and informal channels tend to prevail. The unbanked too call for attention, as that they do not even hold a bank account and hence are excluded from formal banking opportunities, which is likely to pave the way to alternative, less reputable business models. Given the high number of potential consumers involved worldwide, furthering their financial inclusion sounds like a must. In sight of reaching this ambitious goal, the starting point can be identified with an extensive analysis of the underlying concepts, that are closely linked to the Sustainable Development Goals adopted by the United Nations in 2015; the next step revolves around the features of the market segments under investigation, their financial needs that remain unsatisfied and the strategic tools that are likely to improve the state of the art. The main findings lead to stress that usually listed categories to be better served by banks do not tell the whole story, which should act as a stimulus to disseminate best practices and to suggest concrete proposals; they can help to meet the critical challenges of social and economic sustainability within the framework of the generation pact and may also allow financial institutions to expand their activity profitably. Conclusions imply that a more inclusive financial system would provide benefits to the underbanked (not to mention the unbanked), as well as to society at large, with financial competence, literacy and education set to gain momentum.