The aim of this chapter is to investigate the relationship between financial literacy and numeracy. It turns out that numeracy and financial literacy are strongly correlated. In order to clarify this relationship, we review, in a first section, the general definition of numeracy and its most commonly used measures. We then try to enlighten the distinction that can be made between numeracy and financial literacy. In a second section, we focus on the relationship between numeracy and financial literacy using the main empirical studies performed. Since the analyses of their results show that numeracy is a key determinant of financial literacy, we highlight, in a third and final section, the key role that numeracy could have in education programs and consumer protection policies to improve financial decisions.